The cells help blood vessels expand and relax. The impaired regulation in blood flow is a result of the blood vessels not expanding and relaxing normally. If you climb a flight of stairs, you need more blood flow in your coronary arteries to supply your heart with enough oxygen. The blood vessels increase the blood flow by dilating. If the blood vessel cannot dilate as efficiently as it should, the risk of a heart attack increases.
Exercise improves endothelial function and counteracts the problem.
It doesn't seem to be directly related to other well-known risk factors such as high cholesterol or advanced age, but it does appear to aggravate these risks. This suggests an important additional health threat when both genetic and environmental risk factors are combined. Increases in blood flow protect the vascular wall. Alterations of coronary blood flow may speed the formation of atherosclerotic plaques, which restrict blood flow and can cause heart attacks. In the study, the 50 individuals who had a positive family history of premature heart disease had problems even in normal coronary blood vessels that had no atherosclerosis.