This study was undertaken to evaluate the effects of circulatory support on cardiac function in 7 patients. They were 2 men and 5 women with of age 34-54 years; Six patients underwent mitral valve replacement and one had mitral valve plasty. End-systolic pressure/volume (ESP/ESV) representing left ventricular contractility was measured just before ECC starting and after cardiac beating began in the process of rewarming. Measurements were repeated at every, interval of 10 minutes up to 60 minutes. ESP/ESV (mmHg/ml) [% of that before ECC] were as following; before ECC: 1.69 +/- 0.68 (mean +/- SD) [100], after 10 minutes; 0.40 +/- 0.24 [25.1 +/- 13.8], after 20 minutes; 0.52 +/- 0.26 [31.5 +/- 12.9], after 30 minutes; 0.77 +/- 0.28 [47.6 +/- 10.5], after 40 minutes; 0.97 +/- 0.26 [60.5 +/- 11.3], after 50 minutes; 1.18 +/- 0.46 [70.6]8.0], after 60 minutes; 1.36 +/- 0.56[80.4 +/- 12.7]. It took 39.6 minutes to recover up to 69% of that before ECC. These data suggested that the myocardial ischemia associated with aortic cross clamping continued for at least 60 minutes after cardiac beating resumed. We concluded that assist bypass should be applied to those who could not be weaned from ECC despite adequate use of catecholamine and volume loading.