The effect of sublingual (0.2 mg.) nitroglycerin (TNG) was studied in anesthetized dogs before and after coronary occlusion. Coronary artery occlusion was accomplished by embolization of the circumflex branch of the left coronary artery. TNG was administered before embolization and again at one minute, one, two, and six hours after embolization. TNG treatment did not significantly increase the number of arrhythmias or deaths compared to untreated animals with coronary occlusion. Hemodynamic and blood biochemical parameters were measured 5 to 15 minutes after TNG treatment. At this time of measurement, blood pressures (AO, LV, LA, PA, RV, RA), cardiac output, pulmonary and systemic resistances, and left ventricle work were not significantly different in the TNG-treated group compared to the animals with coronary occlusion but no TNG treatment. In the first five minutes after TNG administration, aortic pressure is reduced. Blood samples withdrawn five minutes after TNG treatment are not significantly different from the untreated animals in PO2, PCO2, pH, glucose, lactate, pyruvate, free fatty acids, LDH, CPK, and SGOT. It is concluded that TNG is not detrimental to animals with acute coronary occlusion and that TNG has a transient, short-duration effect.