During which phase of cardiac cycle is coronary blood flow maximum?

Coronary blood flow is maximum during the isovolumetric relaxation phase of cardiac cycle. During this phase, coronary flow is maximum because of maximum fall of coronary vascular resistance or due to minimal compression of coronary aery by myocardium during this period. Must know: Variation of Coronary flow with Cardiac cycle: During the phase of isometric ventricular contraction: coronary flow falls sharply and reaches minimum or even falls below the level of zero due to back flow. During the maximum ejection phase: coronary inflow rises sharply due to the sudden rise of aoic pressure. During the reduced ejection phase: coronary inflow again falls below the previous level. This is because, aoic pressure is falling but myocardium is still compressing the coronary vessel. During isovolumetric relaxation: coronary blood flow rises sharply. Ref: Textbook of Anesthesia for Postgraduates By T. K. Agasti page 109.