Coronary ischemia. The body will try to limit activity in order to decrease ischemia, so some people will feel fatigue or shortness of breath. Also often people have angina or chest pain with activity which limits activity. On the local level small vessels called collateral vessels can grow to bypass the blockage.
Coronary changes. The heart makes a number of changes. As blockages increase in size, the coronary arteries will increase in diameter in an attempt to continue adequate blood delivery. Unfortunately, this only works to a point and after initial compensaton the arteries can dilate no further and the plaque burden becomes increasingly obstructive. The muscle may respond by contracting less vigourously; hibernating.