This article was last reviewed on
This article waslast modified on December 26, 2018.
Overview of the Heart

The heart is a muscular, fist-sized organ that is located in a space called the mediastinum between the two lungs. It continuously pumps blood, beating as many as 100,000 times a day. The blood that the heart moves carries oxygen and nutrients throughout the body and transports carbon dioxide and other wastes to the lungs, kidneys, and liver for removal.

The heart ensures its own oxygen supply through a set of coronary arteries and veins. The heart is also an endocrine organ that produces the hormones atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP), which coordinate heart function with blood vessels and the kidneys.

Internally, the heart is essentially hollow. It is divided vertically into two halves by a septum, and each side of the heart has two internal chambers – an atrium on top and a ventricle on the bottom. Venous blood enters the right side of the heart through the right atrium and is pumped by the right ventricle to the lungs, where carbon dioxide is released and oxygen acquired. Oxygenated blood from the lungs is returned to the left atrium and is pumped by the left ventricle into arteries that carry it throughout the body. 

Four heart valves regulate the direction and flow of blood through the chambers of the heart. It is their opening and shutting that gives the heart its characteristic "lub-dub" beat. The heart muscle itself is called the myocardium. Lining the chambers of the heart and the valves is a membrane called the endocardium. Encasing the outside of the heart is the pericardium – a layered membrane that is fibrous on the outside and serous (fluid-secreting) on the inside. The pericardium forms a protective barrier around the heart and allows it to beat in a virtually friction-free environment.

Accordion Title
About Heart Disease
  • What is heart disease?

    Heart disease is a general term that refers to a variety of acute and chronic medical conditions that affect one or more of the components of the heart. Anything that damages the heart or decreases the heart's supply of oxygen, makes it less efficient, or reduces its ability to fill and pump will disrupt the coordinated relationship between the heart, kidneys, and blood vessels and can harm not only the heart but the rest of the body as well. Heart diseases can be present at birth (congenital) or may be acquired.

    About 600,000 people die of heart disease in the U.S. every year, according to the Centers for Disease Control and Prevention. That is about 1 out of every 4 deaths. Heart disease is the leading cause of death for both men and women.

    Some common diseases of the heart include the following.

    Coronary heart disease (CHD) and coronary artery disease (CAD) are the most common forms of heart disease. They are usually part of a systemic cardiovascular disease (CVD), a narrowing of arteries in the heart and throughout the body over time due to a build-up of fatty deposits that form plaques (atherosclerosis). This narrowing can significantly limit the amount of blood carried by the arteries and decrease the amount of oxygen supplied to the tissues and organs, including the heart. Narrowed or blocked arteries can lead to angina, heart attack or stroke.

    Angina is intermittent chest pain frequently caused by inadequate supply of blood and oxygen to the heart (ischemia). Angina symptoms usually do not appear until most of the blood flow is lost to an area of the heart, when it can cause chest pain upon exercise that worsens in frequency and severity over time. Chest pain that develops at rest or with minimum exertion is called unstable angina.

    Heart attack (myocardial infarction, MI) is death of heart muscle cells due to blockage of blood flow in the coronary arteries that provide cardiac cells with oxygenated blood. This can cause an acute onset of chest pain. The forms of acute onset of chest pain that include heart attacks and unstable angina are called acute coronary syndrome (ACS).

    Congestive heart failure (CHF) is when the heart is less effective at pumping blood or completely filling or emptying the chambers and less able to deliver oxygen to other parts of the body. Blood may back up into the legs, hands, feet, lungs and liver, causing swelling, and the affected person may experience shortness of breath and fatigue. If the cause is temporary, heart failure may also be temporary; however, it usually is a chronic condition that worsens over time but may improve with treatment.

    Cardiomyopathy is an abnormality of the heart muscle itself:

    • Dilated cardiomyopathy—one or more chambers of the heart enlarge or dilate
    • Hypertrophic cardiomyopathy—one or more of the walls of the heart thicken
    • Restrictive cardiomyopathy—occasionally, abnormal material accumulates in the wall of the heart, reducing the flexibility of the walls of the ventricles
    • Ischemic cardiomyopathy--decreased blood flow to the heart
    • Idiopathic cardiomyopathy—no obvious cause

    Myocarditis refers to inflammation of the muscle of the heart. It often presents with a rapid onset of shortness of breath or an irregular heart beat and can cause heart failure to develop quickly.

    Pericardial disease is a disease of the sac surrounding the heart. Pericarditis, an inflammation of the pericardium, may cause increased friction "rub" and pain in the chest cavity.

    Endocarditis is an inflammation of the membrane lining the heart and heart valves.

    Atrial fibrillation is a quivering or irregular heartbeat (arrhythmia) that can lead to blood clots, stroke, heart failure, and other heart-related complications.

    Heart valve conditions may include:

    • Prolapse—part of the heart valve protrudes into the atrium, preventing a tight seal, which may lead to regurgitation (backflow of blood) and an increased risk of endocarditis
    • Stenosis—narrowing of the heart valve opening, which can affect blood flow rate; depending on the valve(s) affected, it is called pulmonary valve stenosis, aortic valve stenosis, or mitral valve stenosis.

    A variety of conditions or factors can cause or contribute to the development of heart disease. Examples include:

    • Alcohol use
    • Amyloidosis—a rare, progressive disorder that occurs when abnormal proteins, called amyloids, are produced and deposited in various organs in the body such as the heart, causing tissue and organ damage
    • Anabolic steroid use
    • Atherosclerosis—deposits made up mostly of lipids form on artery walls, narrowing and hardening the arteries and causing decreased blood flow
    • Autoimmune conditions such as lupus
    • Congenital defects—those present at birth
    • Diabetes
    • Diet, especially when high in saturated fat and cholesterol
    • Drug use, such as cocaine
    • Drugs used to treat cancer or AIDS
    • Exposure to chemicals or toxins, such as mercury
    • High blood pressure (hypertension)
    • Infection caused by bacteria, viruses or fungi
    • Injury or trauma
    • Rheumatic fever—this rarely occurs in the U.S. now
    • Sedentary lifestyle
    • Smoking cigarettes
    • Thyroid dysfunction (under- and overactive)
  • Signs and Symptoms

    Heart diseases may be have a rapid onset (acute) or develop over time (chronic). They may be transient, relatively stable, or progressive. They may cause a variety of signs and symptoms that frequently change and/or worsen over time.

    Chronic heart diseases can have episodes with acutely worsened symptoms; these may resolve on their own or with treatment, persist, or become life-threatening.

    People with early heart disease may experience few or vague symptoms such as:

    • Fatigue
    • Shortness of breath
    • Dizziness
    • Nausea

    However, these symptoms do not indicate the particular type of heart disease present. These symptoms may also be seen with a variety of other conditions.

    As the disease progresses, signs and symptoms may worsen and include additional ones such as:

    • Swelling of feet, legs and/or abdomen
    • Irregular heart beat or changes in the strength of heart contractions (arrhythmia)
    • Chest pain, discomfort or pressure
    • Referred pain that is felt in the left shoulder, arm, back, or jaw
    • Dilation—stretching of one or more of the heart chambers, causing their interiors to become larger because of increased pressure
    • Inability to keep up with increased demands for oxygen and clearance of waste products, such as during physical activity
    • Insufficient contraction—chambers of the heart do not empty or fill completely as the heart pumps blood
    • Ventricular hypertrophy—increased thickness of the walls of the heart, causing a decrease in the size of the chambers and also a decrease in the flexibility of the heart
  • Tests

    The goals of testing for heart disease are to distinguish between symptoms that are heart-related and those that are due to another condition. Testing is ordered to help determine which heart disease is present, to determine whether the disorder is acute or chronic, to monitor a cardiac event that is in progress such as a heart attack, and to determine the severity and extent of the disease.

    Heart disease that is causing few symptoms may be detected during a visit to a health practitioner for nonspecific symptoms such as fatigue. The healthcare provider may order a variety of blood and other tests to investigate possible causes of the person's symptoms.

    Laboratory blood tests

    Screening for risk of cardiovascular disease
    Cardiac risk testing is performed to screen asymptomatic people to help determine their risk of developing coronary heart disease. A cardiac risk assessment is a group of tests and health factors that have been proven to indicate the chance of having a cardiovascular event such as heart attack or stroke. The factors considered include age, family history of heart disease, diet, physical activity, and blood pressure, for example. Laboratory tests may include:

    • Lipid profile (LDL-C,HDL-C, cholesterol, triglycerides)—a group of tests that examine the amount and type of lipids (fats) in the blood
    • hs-CRP—detects low concentrations of C-reactive protein, a marker of inflammation that is associated with atherosclerosis, among other conditions
    • Lp(a)—an additional lipid test that may be used to identify an elevated level of lipoprotein (a), a modification to LDL-C that increases risk of atherosclerosis; the test may be used in conjunction with a routine lipid profile to provide additional information.

    Several other tests are being studied as potential markers for heart disease. See the article on Cardiac Risk Assessment for more on these.

    Diagnosing heart attacks
    When someone presents to the emergency room with a possible heart attack (acute coronary syndrome, ACS), the person is evaluated with a variety of laboratory blood tests and other tests, such as imaging procedures (see below). These are used to determine the cause of the pain and the severity of the condition. Since some treatments for a heart attack must be given within a short period of time to minimize heart damage, an accurate diagnosis must be quickly confirmed.

    Tests for proteins that are released when muscle cells are damaged, often called cardiac biomarkers, are frequently ordered when someone has symptoms of acute coronary syndrome (ACS), such as chest pain, pain in the jaw, neck, abdomen, back, or that radiates to the shoulder or arms, nausea, shortness of breath, and lightheadedness.

    Tests include:

    • Troponin—the most commonly ordered and cardiac-specific of the markers; will be elevated within a few hours of heart damage and remain elevated for up to two weeks
    • CK-MB—one particular form of the enzyme creatine kinase that is found mostly in heart muscle and rises when there is damage to the heart muscle cells; this test has largely been replaced with the troponin test.
    • BNP or NT-proBNP—released by the body as a natural response to heart failure; increased levels of BNP, while not diagnostic for a heart attack, indicate an increased risk of cardiac complications in persons with ACS.

    Tests for other heart diseases

    • BNP—because BNP is also released by the heart when it is stretched, BNP is also measured in those who have swelling of the legs or abdomen or shortness of breath to assist in diagnosis of heart failure.
    • Pericardial fluid analysis—by analyzing the fluid in the sac that surrounds the heart, health practitioners may be able to tell if the heart tissues are inflamed or have been damaged by trauma or infection or whether congestive heart failure has caused fluid to accumulate around the heart
    • Blood culture—may be done to identify infection of the heart (endocarditis)

    More general blood tests that may be ordered include:

    Other evaluations
    A range of other evaluations and tests are used to assess chest pain and other symptoms. These include:

    • A medical history, including an evaluation of risk factors such as age, weight, diabetes, and smoking
    • A physical examination
    • An electrocardiogram (ECG or EKG)—a test that looks at the heart's electrical activity and rhythm
    • Echocardiography—ultrasound imaging of the heart

    Based on the findings of these tests, other procedures may be necessary, including:

    • Stress testing (See a description on the Mayo Clinic website)
    • Chest X-ray
    • CT (computerized tomography) scan
    • Continuous ECG monitoring (sometimes also called Holter monitoring)—the person being tested wears a monitor that evaluates heart rhythm over a period of time.
    • MRI (magnetic resonance imaging)
    • PET (positron emission tomography)
    • Radionuclide imaging
    • Cardiac catheterization—in this procedure, a thin flexible tube is inserted into an artery in the leg and threaded up to the coronary arteries to evaluate blood flow and pressure in the heart and the status of the arteries in the heart.
    • Coronary angiography—X-rays of arteries using a radiopaque dye to help diagnose CAD; this procedure is performed during coronary catheterization.
    • Tilt table test—ordered to evaluate syncope

    For more information on imaging tests, visit

  • Treatment

    Treatment for heart disease depend on the condition and its severity. Acute conditions, such as a heart attack, require prompt medical intervention to minimize heart damage. For chronic conditions, health practitioners may recommend that their affected patients modify their diets, lose excess weight, exercise (under supervision), manage stress, and quit smoking. Conditions such as hypertension and diabetes should be controlled to minimize their affect on the heart. Heart failure often requires treatment with low salt diet and diuretics to try to reduce the amount of fluid accumulating as well as drugs such as digoxin to improve the function of the heart muscle.

    Medications may be necessary to help manage symptoms and control heart diseases. Surgical procedures may be required to bypass blocked arteries, replace defective heart valves, or fix congenital abnormalities. Those with infections may need to take antimicrobial drugs.

    New medications, procedures, and guidelines for addressing heart disease continue to be developed. People living with heart disease should talk to their healthcare provider about the best treatment options for their condition.

View Sources

Sources Used in Current Review

Different Heart Diseases. World Heart Federation. Available online at through Accessed June 24, 2014.

Diseases and Conditions: Hypothyroidism. Mayo Clinic. Available online at through Accessed June 24, 2014.

Heart Information Center: Heart Anatomy. Texas Heart Institute available online at through Accessed June 25, 2014.

(July 7, 2014) Heart Disease Facts. Centers for Disease Control. Available online at through Accessed August 2014.

McGrath, Monica Forero, et. al. 2005. The endocrine function of the heart. Trends in Endocrinology & Metabolism. Vol. 15., Issue 10.

What is Atrial Fibrillation? American Heart Association. Available online at through Accessed June 25, 2014.

Sources Used in Previous Reviews

Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].

Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.

(2003 October 2, Updated). Facts About Coronary Heart Disease. National Heart, Lung, and Blood Institute (NHLBI) [On-line information]. Available online at through

Toscano, J. (2003 March 11, Updated). Angina: A Patient Guide. [On-line Patient Guide]. Available online at through

(1994) When You Need to Have a Stress Test: A Patient Guide. [On-line Patient Guide]. Available online at through

(2001 August 31). Angioplasty: A Patient Guide. [On-line Patient Guide]. Available online at through

Cardiac Catheterization: A Patient Guide. [On-line Patient Guide]. Available online at through

Toscano, J. (2003 March 11). Cardiac Enlargement: A Patient Guide. [On-line Patient Guide]. Available online at through

(2001 August 28). Congestive Heart Failure: A Patient Guide. [On-line Patient Guide]. vailable online at through

Mayo Clinic Staff (2003 May 29). Chest X-rays: Helping detect heart and lung conditions. [On-line information]. Available online at through

Cardiovascular Disorders, [General]. The Merck Manual of Diagnosis and Therapy, Section 16, Chapter 202. Coronary Artery Disease [On-line information]. Available online at through

Congenital Anomalies. The Merck Manual of Diagnosis and Therapy. Section 19. Pediatrics, Chapter 261. [On-line information]. Available online through

Infective Endocarditis. The Merck Manual of Diagnosis and Therapy. Section 16. Cardiovascular Disorders, Chapter 208. Endocarditis [On-line information]. Available online through

What is Heart Failure. National Heart, Lung, and Blood Institute (NHLBI) [On-line information]. Available online at through

What is Coronary Artery Disease. National Heart, Lung, and Blood Institute (NHLBI) [On-line information]. Available online at through

What is a Heart Attack? National Heart, Lung, and Blood Institute (NHLBI) [On-line information]. Available online at through

A.D.A.M., Updated (2003 February 27, Updated). Heart disease. MedlinePlus Medical Encyclopedia [On-line information]. Available online at

Robert H. Christenson, Ph.D., DABCC, FACB. Professor of Pathology, Professor of Medical and Research Technology Director, Rapid Response Laboratories, University of Maryland School of Medicine, Baltimore, Maryland.

Tanser, P. (2006 February, Revision). Effects of Aging. Merck Manual of Medical Information – Second Home Edition [On-line information]. Available online at through Accessed on 6/28/07.

Tanser, P. (2006 February, Revision). Heart. Merck Manual of Medical Information – Second Home Edition [On-line information]. Available online at through Accessed on 6/28/07.

(2007 February 09, Review). About Heart Disease. CDC [On-line information]. Available online at through Accessed on 6/28/07.

(2007 February 09, Review). Heart Disease Risk Factors. CDC [On-line information]. Available online at through Accessed on 6/28/07.

(2007 February 09, Review). Heart Disease Signs and Symptoms. CDC [On-line information]. Available online at through Accessed on 6/28/07.

Desvigne-Nickens, P, (2007 February, Reviewed). Heart Disease, Frequently Asked Questions. [On-line information]. Available online at through Accessed on 7/9/07.

(2005 August 5). Cardiovascular disease 101: Know your heart and blood vessels. [On-line information]. Available online at through Accessed on 7/9/07.

(2005 November, Revision). Cardiovascular Tests and Procedures, Introduction, Cardiac Catheterization, Coronary Artery Bypass Grafting, Echocardiography, Electrocardiography, Electrophysiologic Studies, Imaging Tests, Percutaneous Coronary Interventions, Radionuclide Imaging, Stress Testing, Tilt Table Testing. Merck Manual for HealthCare Professionals [On-line information]. Available online at through Accessed on 7/9/07.

(Updated 2011 January 26). What is Cardiovascular Disease. American Heart Association [On-line information]. Available online at through Accessed April 2011.

Boudi, F.B. (Updated 2011 March 29). Risk Factors for Coronary Artery Disease. Medscape Reference [On-line information]. Available online at through Accessed April 2011.

Roberts, W. (Updated 2011 February). Cardiovascular Disease (Traditional Risk Markers) - Risk Markers - CVD (Traditional). ARUP Consult [On-line information]. Available online at through Accessed April 2011.

Delgado, J. et. al. (Updated 2011 February). Cardiovascular Disease (Non-traditional Risk Markers) - Risk Markers - CVD (Non-traditional) ARUP Consult [On-line information]. Available online at through Accessed April 2011.

Mayo Clinic Staff (2011 January 12). Heart Disease. [On-line information]. Available online at through Accessed April 2011.

Riaz, K. and Aqeel, A. (Updated 2011 March 29). Hypertensive Heart Disease. Medscape Reference [On-line information]. Available online at through Accessed April 2011.

Nghiem, H. (2011 February 18). Threshold for 'High Risk' Reduced in New AHA Guidance on CVD Prevention for Women CME. Medscape Education from Heartwire CME [On-line information]. Available online at through Accessed April 2011.

Siemens. High Sensitivity C-Reactive Protein (hsCRP) Assay. Available online at through Accessed September 2011.