The efficacy of cold crystalloid cardioplegia (St. Thomas II solution) during aortic cross-clamping more than 240 minutes was evaluated in 5 patients with non-coronary diseases undergoing heart surgery. The ischemic time ranged from 257 to 302 minutes with the mean of 274 minutes. As the technique of myocardial protection, multidose antegrade crystalloid cardioplegia was used at an interval of 20 minutes. These patient were compared with another patient group with clamping time 120-180 minutes. There was no difference between the two groups in terms of mortality, cardiac index, CK, CK-MB, GOT, LDH. These findings suggest that cold crystalloid cardioplegia provided clinically satisfactory myocardial protection during the aortic cross-clamping for more than 240 minutes.