Topographic changes in the completely healed (6 weeks) left ventricle of the rat, caused by early (30 minutes) and delayed (90 minutes) coronary artery reperfusion, were examined. With early reperfusion the extent of the scar, as a percentage of left ventricular (LV) circumference, was reduced compared to the extent of the scar in rats with permanent occlusion (27 +/- 3% vs 42 +/- 2%, p less than 0.01). Early reperfusion also preserved LV topography by preventing dilation of the LV cavity and thinning of the healed free wall. Late reperfusion (90 minutes) did not reduce the extent of the scar (35 +/- 3% vs 42 +/- 2% of LV circumference, p = NS) or prevent dilation of the LV cavity compared with permanent occlusion. However, the healed free wall/noninfarcted septum ratio was significantly greater in rats with late reperfusion than in those with permanent occlusion (0.98 +/- 0.06 vs 0.73 +/- 0.07, p less than 0.05). Thus early reperfusion completely inhibited scar thinning and dilation of the LV cavity, maintaining normal LV topography. Late reperfusion, too late to reduce infarct size, still contributed to improved healing of the myocardium by resulting in a thicker scar.