Cardiovascular disease is the number-one cause of death in the United States and in most other industrial societies. Most often death results from some complication of atherosclerosis (hardening of the arteries as a result of lipid and calcium deposition). Although it can affect almost any artery, the disease most often develops in the aorta and in the coronary and cerebral arteries. When it occurs in the cerebral arteries, it can lead to a cerebrovascular accident (CVA), commonly referred to as a stroke.

Although there is apparently no single cause of atherosclerosis, several major risk factors have been identified:

1. Elevated cholesterol levels in the blood, often associated with diets rich in total calories, total fats, saturated fats, and cholesterol.
2. Hypertension. The higher the blood pressure, the greater the risk.
3. Cigarette smoking. The risk of developing atherosclerosis is two to six times greater in smokers than in nonsmokers and is directly proportional to the number of cigarettes smoked daily.
4. Diabetes mellitus, and endocrine disorder in which glucose is not metabolized normally.

The risk of developing atherosclerosis also increases with age. Estrogen hormones are thought to offer some protection in women until after menopause, when the concentration of these hormones decreases. Other suggested risk factors currently being studied are obesity, hereditary predisposition, lack of exercise, stress and behavior patterns, and dietary factors.

In atherosclerosis, lipids are deposited in the smooth muscle cells of the arterial wall. These cells proliferate, and the inner lining thickens. More lipid, especially cholesterol from low-density lipoproteins, accumulates in the wall. Eventually calcium is deposited there, contributing to the slow formation of hard plaque. As the plaque develops, arteries lose their ability to stretch when filled with blood, and they become progressively occluded (blocked). As the artery narrows, less blood can pass through to reach the tissues served by that vessel, and the tissue may become ischemic (lacking in blood). Under these conditions the tissue is deprived of an adequate oxygen supply.

When a coronary artery becomes narrowed, ischemic heart disease can develop. Sufficient oxygen may reach the heart tissue during normal activity, but the increased need for oxygen during exercise or emotional stress results in the pain known as angina pectoris. Persons with this condition often carry nitroglycerin pills for use during an attack. This drug dilates veins, reducing venous return. Cardiac output is lowered so that the heart is not working so hard and requires less oxygen. Nitroglycerin also dilates the coronary arteries slightly, allowing more blood to reach the heart muscle.

Myocardial infarction (MI), popularly referred to as heart attack, is a very serious, often fatal, consequence of ischemic heart disease. MI often results from a sudden decrease in coronary blood supply. The portion of cardiac muscle deprived of oxygen dies within a few minutes and is then referred to as an infarct. MI is the leading cause of death and disability in the United States. Just what triggers the sudden decrease in blood supply is a matter of some debate. It is thought that in some cases an episode of ischemia triggers a fatal arrhythmia such as ventricular fibrillation, a condition in which the ventricles contract very rapidly without actually pumping blood. In other cases, a thrombus (clot) may form in a diseased coronary artery. Because the arterial wall is roughened, platelets may adhere to it and initiate clotting.

If the thrombus blocks a sizable branch of a coronary artery, blood flow to a portion of heart muscle is impeded or completely halted. When this condition, referred to as a coronary occlusion, prevents blood flow to a large region of cardiac muscle, the heart may stop beating – that is, cardiac arrest may occur – and death can follow within moments. If only a small region of the heart is affected, however, the heart may continue to function. Cells in the region deprived of oxygen die and are replaced by scar tissue.