In "left-sided" cardiac diseases, the effects of nitroglycerin on arterial pressure and heart rate were noted to be modest and disappeared within 15 minutes whereas the effect upon venous pressure, measured on the median cubital vein, lasted for approximately 30 minutes. 2) At 30 minutes after a dose of nitroglycerin there occured a significant depression of venous pressure elevation on exertion in patients with such "left-sided" cardiac diseases as ischemic heart disease, arteriosclerotic heart disease and hypertensive cardiovascular disorder. In patients with mitral insufficiency and aortic stenosis, on the other hand, the exertional venous pressure elevation was significantly suppressed 7 minutes after nitroglycerin although the suppression did not longer exist 30 minutes after administration. 3) The arterial pressure, heart rate, resting venous pressure and venous pressure elevation on exertion were virtually not affected by the administration of nitroglycerin in "right- or both-sided" cardiac disorders. 4) There was no significant change in cardiac output 30 minutes after a sublingual dose of nitroglycerin. The data obtained seem to stress importance of the effect of dilating capacitance vessels in the mechanism of antianginal action of nitroglycerin.