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Dynamics of the coronary collateral circulation have been investigated by means of the retrograde flow technic. A principal determinant of retrograde flow appears to be the perfusion pressure irrespective of the rate of coronary inflow. Nitroglycerine, histamine and norepinephrine failed to augment retrograde flow. Reactive hyperemia and temporary myocardial ischemia resulted in a reduction of retrograde flow which could be due to active vasoconstriction or to myocardial stretching. Changes in heart rate and the onset of ventricular fibrillation did not alter retrograde flow, but low blood viscosity increased it.

Some Determinants of Coronary Collateral Blood Flow in the Open-Chest Dog