While the larger arteries in the heart are responsible for pumping blood through your heart, the small vessels expand when you're active and then contract while you're at rest.

The large vessels in your heart can become narrowed or blocked through atherosclerosis, a condition in which fatty deposits build up in the arteries. In small vessel disease, the narrowing of the small vessels in the heart makes it so they can't expand properly when you're active. As a result, you don't get an adequate supply of oxygen-rich blood. This inability to expand is called endothelial dysfunction. This problem may cause your small vessels to actually become smaller when you're active or under emotional stress. The reduced blood flow through the small vessels causes chest pain and other symptoms similar to those you'd have if you were having angina or a heart attack.

Apr. 09, 2013