The purpose of this study is to clarify the effects and limitation of high-dose therapy with dopamine (DOP) and dobutamine (DOB) for the patients with severe low cardiac output syndrome (LOS) after coronary artery bypass grafting (CABG). Among the patients who underwent CABG in Sendai Tokusyukai Hospital between 1986 and 1991, two groups were selected: More than 20μg/kg/min of both DOP and DOB were administered within 48 hours after CABG in “high-dose group” patients (n=6); Less than 5μg/kg/min of DOP and DOB were administered in the same period in “low-dose group” patients (n=9). All patients in the high-dose group had episodes of acute myocardial infarction in the pre- or intra-operative period. The operative mortality rate of this group was 34% (2/6). Significant stenoses of the left main trunk were observed preoperatively in both dead cases. The postoperative changes of cardiac index, heart rate, serum CPK-MB, dose of lidocaine given, urine output, total peripheral resistance and incidence of cardiac arrhythmia within 48 hours after CABG were compared between the two groups. There were no significant differences in all parameters except cardiac index, heart rate and total dose of lidocaine. However the maximal value of the mean heart rate in high-dose group was less than 120beats/min and lidocaine was effective in all patients with premature ventricular contraction. We conclude that high-dose therapy with DOP and DOB is useful for the selected patients with severe LOS after CABG when side effects caused by these drugs are carefully managed.