The purposes of this study were to demonstrate that echocardiography can be used to demonstrate the systolic wall thinning of acutely ischemic myocardium, and to compare the effects of nitroglycerin and nitroprusside on systolic thinning, wall stress and perfusion of ischemic myocardium. In 37 dogs, the ratio of end-systolic-to-end-diastolic posterior wall thickness fell from 1.30 +/- 0.02 to 0.88 +/- 0.01 ((p less than 0.001) after circumflex coronary occlusion; perfusion of the area supplied by the occluded artery fell from 98.2 +/- 7.5 ml/100 g/min to 36.5 +/- 2.9 ml/100 g/min (p less than 0.001). Nitroglycerin and nitroprusside were given to lower mean arterial pressure by 7% and 15%. Despite the reduction in coronary perfusion pressure, transmural perfusion, endocardial/epicardial perfusion ratio and systolic thinning remained constant. Both drugs reduced the ischemic "wall stress index" (ventricular pressure x ventricular diameter/wall thickness) by almost 50%. Thus, both nitroglycerin and nitroprusside were equally beneficial in this model of acute myocardial ischemia.