H

heart The organ that pumps BLOODand main-
tains circulation. About the size of a closed fist, the
heart resides in the chest between the LUNGS,
slightly offset to the left behind the protective
STERNUM(breastbone). It begins beating at about 3
weeks gestational age and during a typical life
time contracts about 2.5 billion times. The heart’s
four chambers contract in coordinated sequence to
pump blood to the lungs and to the body, circulat-
ing the body’s 5- to 6-liter blood supply through
the network of arteries and veins of the cardiovas-
cular system up to three times a minute. Synchro-
nized electrical impulses orchestrate the con-
tractions. One-way valves direct the flow of blood
into, through, and out of the heart. The right
heart handles deoxygenated blood; the left heart
handles oxygenated blood.

HEALTH CONDITIONS THAT CAN AFFECT THE HEART
ANEURYSM AORTIC STENOSIS
ARRHYTHMIA ATRIAL FIBRILLATION
BUNDLE BRANCH BLOCK CARDIAC ARREST
cardiac tamponade CARDIOMYOPATHY
CONGENITAL ANOMALY CONGENITAL HEART DISEASE
CORONARY ARTERY DISEASE(CAD) ENDOCARDITIS
FIBROELASTOMA HEART ATTACK
HEART FAILURE HYPERTENSION
LONGQT SYNDROME(LQTS) MYOCARDITIS
MYXOMA PALPITATIONS
PAROXYSMAL ATRIAL TACHYCARDIA(PAT) PERICARDITIS
PREMATURE VENTRICULAR RHEUMATIC HEART DISEASE
CONTRACTION(PVC) TORSADE DE POINTES
SICK SINUS SYNDROME VALVULAR HEART DISEASE

The heart’s blood supply comes from the CORO-
NARY ARTERIES, which arise from the root of the
AORTAand encircle the heart. The heart has a sub-
stantial oxygen appetite; the coronary arteries

deliver 20 percent of the body’s blood supply and

70 percent of the blood’s oxygen content to the

heart. The heart is a remarkably sturdy and reli-

able structure that can withstand significant dam-

age and still function adequately to supply the

body’s needs for oxygen and other nutrients.

For further discussion of the heart within the

context of cardiovascular structure and function,

please see the overview section “The Cardiovascu-

lar System.”

See also LIFESTYLE AND CARDIOVASCULAR HEALTH;

RISK FACTORS FOR CARDIOVASCULAR DISEASE.

heart attack The interruption of cardiovascular

function. The most common cause of HEARTattack is

MYOCARDIAL INFARCTION, a blockage of the CORONARY

ARTERIES, usually with a BLOODclot, that disrupts the

flow of blood to the heart (MYOCARDIUM). Other

causes of heart attack include ARRHYTHMIA, systemic

HYPOXIA(such as may occur with drowning or car-

bon monoxide poisoning), and ELECTROCUTION.

About 1.3 million Americans experience heart

attacks each year, and 40 percent of them die as a

result. Health experts believe significantly more

people could survive heart attack with early treat-

ment. Up to 60 percent of people who die from

heart attack do so before ever reaching a hospital.

When symptoms suggest heart attack:

• Call 911


• If the person is conscious, have him or
  her chew an aspirin


• If the person is unconscious, has no
  PULSEor is not BREATHING, begin CAR-
  DIOPULMONARY RESUSCITATION(CPR)


• Continue CPR until medical help
  arrives

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