A B S T R A C T After acute coronary occlusion in primates, the time period during which reperfusion results in significant salvage of reversibly injured myocardium was investigated. In 23 monkeys, the left anterior descending coronary artery was occluded from 1 to 6 h; and in 5 others, occlusion was maintained for the 1-wk study. Unipolar epicardial electrocardiograms were monitored from mapping points on the anterior and lateral left venticle. S-T segment elevation (S-Tt) and R + S wave amplitude (RS) were measured before occlusion and at regular intervals during occlusion and reperfusion. Summated S-Tt (2S-Tt) and summated RS (IRS), computed for mapping points demonstrating greater than 2 mV S-Tt, were used as serial measures of electrical injury. IS-Tt peaked within 2-h postocclusion and then gradually declined throughout the period of occlusion suggesting the progress of infarction within the area of injury. After reperfusion ZS-Tt rapidly declined to near cnotrol values indicating the extent of reversible injury. During the period of occlusion, the magnitude of voltage loss in ZS-Tt as a percent of maximum ZS-Tt was proportional to the duration of occlusion, though the rate of loss decreased with increasing time of occlusion. Reperfusion after 6 h of occlusion resulted in reversal of only a small remaining component of the maximum current of injury. The voltage decrease in IRS (from control values) was proportional to the duration of occlusion, though the decrease was accelerated during the first 2-h postocclusion. Whereas reperfusion interrupted the decline in ZRS, a consistent increase in ZRS postreperfusion was observed only after occlusion of 1 h. With respect to reperfusion groups, significance in 2S-Tf voltage loss as a percent of maximum

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