The effects of 1 hour, 3 hours and 10 days coronary artery reperfusion after 20 minutes, 40 minutes, 3 hours, 4 hours and 5 hours coronary artery occlusion on the contractility of myocardium was studied by the strain gauge arch, and the myocardial changes was also studied histologically. Results obtained were follows. In the short term reperfusion study: 1) Dyskinesis disappeared in all cases if reperfusion was begun after 20 minutes of ischemia. 2) Dyskinesis remained in all cases if reperfusion was begun after 40 minutes of ischemia. In the long term reperfusion study: 3) Dyskinesis disappeared in all cases after 10 days reperfusion with 3 and 4 hours ischemia groups, and the recovery of myocardial contractility was good. 4) Dyskinesis remained in 2 of 5 dogs with 5 hours coronary occulusion even after 10 days of reperfusion, and the recovery of myocardial contractility in 3 of 5 dogs with this group was poor. It is concluded that revascularization of myocardium that has been kept ischemia for less than 4 hours may lead to disappearance of dyskinesis and recovery of myocardial contractility. These findings also indicate that early coronary revascularization does not always provide an immediate recovery of dyskinesis of the revascularized area.