Exercise Dilates Coronary Arteries

Coronary arteries have two main potential sites of resistance to blood flow. Normally the small arteries (arterioles) buried within the heart muscle are the major resistance to blood flow. Arterioles act as tiny valves which open when the heart needs more blood flow such as during exercise. The large epicardial arteries (on the heart's surface) can become obstructed by plaque and offer another increased resistance. All blood vessels are lined with endothelium which among other factors is sensitive to the velocity of blood flow; the higher the blood flow (shear stress on the wall) the healthier they are and the more nitric oxide they release. In the study below acetylcholine injections are used to test the ability of the endothelium to release nitric oxide. Normal arteries dilate in response to acetylcholine but dysfunctional arteries don't respond; they might even contract.

Exercise causes an increase in coronary blood flow by dilating the arteriolar valves. The increased shear stress on the endothelium makes it healthier and dilates both the large epicardial arteries and increase maximum coronary blood flow. Hippocrates was right 2400 years ago.

While exercise will not shrink atherosclerotic plaque, it will keep the parts of the large arteries not involved with plaque more dilated and help to maintain higher blood flow to the heart.