Effect of right atrial pacing and nitroglycerin on myocardial oxygen balance.

The direct effects or right atrial pacing and nitroglycerin on myocardial oxygen balance were studied in isolated canine hearts. Whereas atrial pacing produced an increase in myocardial oxygen consumption (MVO2) and no change in the affinity of hemoglobin for oxygen (P-50), an intracoronary infusion of nitroglycerin decreased both MVO2 and the affinity of hemoglobin for oxygen (increased P-50) in coronary venous blood. Under conditions of a constant coronary blood flow, nitroglycerin may benefit a hypoxic myocardium by reducing oxygen demand and by increasing availability of oxygen for rapid diffusion to tissue by increasing P-50.