Final answer:
During systole, the contraction phase of the cardiac cycle, the coronary blood flow is reduced due to compression of the coronary arteries, especially in the left ventricle myocardium. Diastole allows for the replenishment of blood flow to these vessels.
Step-by-step explanation:
The part of the heart that experiences a reduction in coronary blood flow during systole is the ventricular myocardium, particularly in the left ventricle. During systole, which is the contraction phase of the cardiac cycle, the ventricles are pumping blood into the arteries. This vigorous contraction compresses the coronary arteries embedded in the heart muscle, momentarily reducing the flow of oxygen-rich blood to the cardiac muscle cells or myocardium. Diastole, on the other hand, is the relaxation phase, when the heart muscle is relaxed, allowing the ventricles to refill with blood and the coronary vessels to receive increased blood flow. Plaque accumulation in a coronary artery further exacerbates this condition by reducing blood flow, which can starve the heart muscle of oxygen, potentially leading to conditions such as angina or myocardial infarction.