The Normal Heart
The heart is a fist-sized muscle that pumps blood through the body 24 hours a day, 365 days a year, without rest. The normal heart is made up of four parts: two atria on the top of the heart (right atrium and left atrium), and two ventricles (right ventricle and left ventricle) which are the muscular chambers on the bottom of the heart that provide the major power to pump blood.
These four chambers are connected by valves that allow blood to move forward and prevent it from flowing backwards. Coronary arteries, or blood vessels, deliver a constant, nourishing supply of blood to the heart muscle itself.
The heart’s pumping action, or “heartbeat,” is directed by a complicated electrical system. Problems with the regular heartbeat, such as abnormally fast or slow rhythms, can be caused by a heart attack(myocardial infarction) or aging, but may happen for other reasons as well. Heart rhythm problems can cause the feeling that the heart is “racing,” or "skipping" (palpitations), weakness, shortness of breath, passing out (syncope), and sometimes death.
Blockages in the coronary arteries can also cause major problems in the heart because they slow or stop the flow of blood to the heart muscle. If the heart does not get enough blood, pain (often called angina) or muscle death from a heart attack (myocardial infarction) can result which can damage the heart's ability to pump and cause abnormal heart rhythms.
Although people can do a great deal to protect their hearts by exercising regularly, eating a healthy diet, maintaining a healthy weight, not smoking, and controlling their cholesterol and blood pressure, some people are born with a tendency to have heart disease or have other illnesses that may affect the heart.