Two cases of acute aortic dissection which developed compression of the true lumen due to retrograde perfusion during cardiopulmonary bypass were reported. In the first case, coronary reperfusion could not be achieved when the aortic cross-clamping was removed after Collins' method of aortic dissection. There was no blood flow from the true lumen through the aortic root while the false lumen was distended by the retrograde perfusion. After completion of antegrade perfusion through the arterial cannula inserted into the anastomosed site of the ascending aorta, coronary reperfusion was established and the heart beating could be thereby obtained. In the second case, the false lumen was gradually expanded, and the true lumen was completely obstructed by it. Reexpansion of the true lumen was achieved by initiation of antegrade perfusion through the cannula inserted into the graft replaced in the ascending aorta. Fortunately cerebral and cardiac complications were not found in both cases postoperatively. Compression of the true lumen is rare, but fatal complication that may occur during retrograde perfusion in surgical repair for aortic dissection of Stanford type A. Therefore, it is very important to replace the perfusion cannula in the true lumen of the reconstructed aorta for preventing insufficiency of coronary and cerebral circulation.