Complex sentence: The vessels that deliver oxygen-rich blood to the myocardium are the coronary arteries, the arteries, when healthy, are capable of autoregulation to maintain coronary blood flow at levels appropriate to the needs of the heart muscle.
Split into simpler sentences: The vessels that deliver oxygen-rich blood to the myocardium are the coronary arteries. The arteries, when healthy, are capable of autoregulation to maintain coronary blood flow at levels appropriate to the needs of the heart muscle.