Effect of cardiac contraction on coronary blood flow.

In the experimental animal the basic and controversial problem was studied of the influence of cardiac contraction on coronary blood flow. Normally beating hearts were perfused at a constant pressure, and coronary inflow and outflow were determined. In order to assess the role of systole, prolonged periods of ventricular asystole and fibrillation were induced and observations were made of the changes in coronary flow. With the cessation of cardiac contraction blood flow in the coronary arteries and coronary sinus rose appreciably. The results of these studies support the concept that contraction of the heart muscle, by compression of the myocardial vascular bed, behaves as a throttling mechanism and impedes coronary flow. The method employed permits a separation and quantitation of the effects on coronary flow resulting from cardiac contraction and the vasomotor state of the coronary vessels.