Which phase predominantly governs coronary perfusion for the LV?

• A. Systole.
• B. Diastole.
• C. Both phases equally.
• D. Only during atrial contraction.

Answer: (B)

The main concept here is that blood flow to the left ventricle’s coronaries happens mostly during diastole. When the LV contracts in systole, the thick muscular wall and high intramyocardial pressure compress the coronary vessels, especially the subendocardial vessels, which drastically limits flow. In diastole the heart relaxes, intramyocardial pressure falls, and the aortic pressure gradient drives blood through the coronary arteries into the LV myocardium. Because diastole provides the window of low vascular resistance and ongoing perfusion, it dominates LV coronary flow. If heart rate increases and diastolic time shortens, coronary perfusion to the LV can drop, risking ischemia. Atrial contraction adds some filling during diastole but is not the primary driver of LV coronary flow.