A coronary artery and the accompanying vein were ligated temporarily for 30, 60 and 120 minutes in 39 cats. By labelling the blood with the fluorescent dye acridine orange, the intravital blood supply of the myocardium was investigated 5 minutes to 6 hours after release of the ligature. The region supplied by the temporarily ligated coronary artery (RSCA) was demonstrated by postmortal perfusion of this vessel using the dye light green. Resumption of circulation in the deeper layers of the RSCA was delayed after a prior coronary occlusion, even occasionally after occlusions lasting only 30 minutes. After a coronary ligation of 60 to 120 minutes the inner layers of the RSCA became the sites of prolonged disturbance of blood supply. The circulatory abnormality observed immediately following release of the ligature did not result from intraluminal vascular obstruction. Even after a temporary ischemia lasting 120 minutes it was still possible, immediately after removal of the liga-ture, to perfuse an intravitally ischemic portion of the RSCA. The significance of these results for the determination of the so-called "revival-time" of the cardiac muscle is pointed out. ADDITIONAL KEY WORDS temporary cardiac ischemia intravital staining acridine orange coronary perfusion intracellular and interstitial edema revival-time of cardiac muscle anesthetized cats • After temporary interruption of the coronary circulation, survival of the myocardium depends primarily on whether a sufficient blood supply is established before irreversible injury has occurred. Detailed studies of the resumption of circulation in the myocardium after temporary occlusion of coronary vessels have not been done, so far as we know. Therefore, we examined the circulation in involved myocardium after a coronary artery had been occluded temporarily for 30, 60 or 120 minutes. Moreover, we wished to determine whether it might be possible to perfuse the myocardial vessels artificially in a region of prior ischemia. Methods Thirty-nine cats weighing 1.5 to 2.5 kg and unselected, were anesthetized with sodium pento-barbital (25 mg/kg). Respiration was maintained through an endotracheal tube attached to a respirator pump. Arterial pressures were monitored continuously by a Statham strain gauge attached to a catheter in the femoral artery. Left thoracot-omy and pericardotomy incisions remained un-closed throughout the experiment. The anterior descending branch of the left main coronary artery (together with the accompanying vein) was ligated temporarily 2 to 3 mm distal to its origin. The duration of coronary ligation was 30, 60 or 120 minutes after which the ligature was removed , allowing resumption of coronary flow for periods of five minutes to six hours before the beating heart was excised for study. Table 1 lists the experiments done and the number of animals in each category.

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