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A simple method for simulating indicator-dilution curves produced by shunts in intact dog is described. Simulated right to left shunts of about 2.5 per cent can be clearly detected in peripheral arterial dilution curves. A larger simulated left to right shunt was required to produce clear-cut distortion of the systemic arterial indicator-dilution curve. For detection of a small left to right shunt, sampling from both the pulmonary and the femoral artery simultaneously gives indicator-dilution curves which are much more sensitive.

1. 1. Hemodynamic studies, including the determination of cardiac output and coronary blood flow, have been made before and after the intravenous administration of diazoxide to anesthetized intact dogs and unanesthetized man. The response was essentially the same in the dog and in man. 2. 2. Administration of this agent intravenously was accompanied by an acute reduction in peripheral, total pulmonary, and coronary resistances, with a decrease in systemic and pulmonary arterial pressures and an increase in cardiac output and coronary blood flow. 3. 3. Coronary sinus oxygen content increased, with the per cent increase in coronary blood flow significantly greater than the change in cardiac rate, left ventricular work, and left ventricular oxygen consumption. 4. 4. The acute hemodynamic effects of diazoxide in control animals are not significantly different from the effects in animals pretreated with chlorothiazide or small doses of reserpine. 5. 5. Although both diazoxide and chlorothiazide are benzothiadiazine derivatives, their acute hemodynamic effects differ greatly.