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Nitroglycerine administered intravenously to dogs under chloralose anesthesia elicits a biphasic effect. During the first phase, it causes an increase in heart rate, a decrease in mean arterial bloodpressure and a rise in cardiac output, coronary blood flow and myocardial oxygen consumption. During the second phase, the heart rate remains elevated and the arterial bloodpressure remains below control, but cardiac output, coronary blood flow and myocardial oxygen consumption decrease to or below control values. During both phases, the myocardial oxygen arteriovenous difference is decreased below its control value because of a rise in the oxygen content of the coronary sinus blood. It is concluded that nitroglycerine first increases the myocardial oxygen consumption less than the coronary blood flow, then may decrease the oxygen consumption more than the coronary flow.

Doses of aminophylline commensurate with human doses, administered intravenously to dogs under chloralose anesthesia cause an increase in heart rate, a decrease in mean systemic arterial blood pressure, a rise in cardiac output, coronary blood flow and myocardial oxygen consumption and an increase in the oxygen content of the coronary sinus blood which resulted in a decrease in the coronary oxygen arteriovenous difference as the oxygen content of the arterial blood remained essentially unchanged. This increase in coronary blood flow in the presence of a decrease in arterial blood pressure is obviously due to a decrease in the resistance of the coronary bed, which is probably due, at least partially, to dilatation of the coronary bed. Furthermore, since aminophylline decreases the coronary oxygen arteriovenous difference although it raises the myocardial oxygen consumption, it is concluded that aminophylline increases the coronary blood flow more than the myocardial oxygen consumption.