The effects of 15 min periods of coronary occlusion on global and regional myocardial function, plasma creatine kinase (CK) and isoenzyme MB CK activity and subsequent myocardial necrosis were studied in 15 conscious dogs and 9 conscious baboons. Overall left ventricular (LV) function was assessed with measurements of LV systolic and diastolic pressures, rate of change of LV pressure, LV dP/dt. Regional LV function was assessed with measurements of regional segment length and velocity of shortening and/or regional LV wall thickening. An implanted hydraulic occluder on either the left anterior descending or circumflex coronary artery was inflated for 15 min. This induced complete loss of segment length shortening and systolic wall thickening (ultrasonic transit time technique). With release of the occlusion and reperfusion, recovery of regional mechanical function was delayed, but did occur after 6 hrs. Serial plasma enzyme activity revealed a significant increase in total CK as well as MB CK. At autopsy, neither gross pathological evidence (TTC-technique) nor histological evidence of myocyte necrosis was observed. Thus, in the conscious dog as well as in the conscious baboon, short episodes of intense myocardial ischemia do not result in a permanent deficit of myocardial function or necrosis. However, during the early phase of reperfusion, significant depression of regional mechanical function is observed associated with significant appearance of total CK and MB CK in the blood.