To obtain insights into transmural myocardial perfusion during coronary artery stenosis, we evaluated the characteristics of septal arterial blood flow velocity using a 20 MHz multichannel pulsed Doppler velocimeter. Septal arterial blood flow velocity was characterized by the presence of a retrograde blood velocity component. Thus, a substantial amount of blood that entered the myocardium during diastole flows backward to the proximal coronary arteries. This is evidence of the coronary slosh phenomenon. With coronary artery stenosis, the systolic retrograde flow was enhanced, and was augmented further by coronary vasodilation. Since the component of blood moving backward in systole does not contribute to the perfusion of the myocardial bed, an augmented coronary slosh phenomenon plays an important role in disturbing myocardial inflow in addition to the stenotic impeding effects on diastolic flow.