We evaluated the efficacy of the cardioplegic myocardial protection by combining antegrade cardioplegic induction via the aortic root with retrograde cardioplegia via the coronary sinus in patients who had LAD stenosis or occlusion with collateral circulation. In study I, forty-six patients were divided into two groups: antegrade group (group A; 32 cases), which were perfused by only antegrade fashion via the aortic root, and bi-directional group (group B; 14 cases), which were perfused by combining antegrade with retrograde fashion. In study II, patients were divided into four groups: 32 cases in group A were divide into three subgroups by the direction of the collateral circulation to LAD in preoperative coronary angiograms: group I (antegrade collateral circulation; 18 cases), group II (retrograde collateral circulation; 7 cases), group III (99% stenosis with delayed filling; 7 cases) and group B was as group IV. Myocardial injury was assessed with the use of enzyme indexes (total CPK, CPK-MB, %MB, peak CPK, peak CPK-MB and peak % MB) in study I and study II. There was no significant difference between the two groups in study I and the four groups in study II in terms of patients' profile, graft materials, number of grafts, aortic cross-clamping time, total cardiopulmonary bypass time and surgical results. Total CPK level in group B was significantly lower (p < 0.05) compared with group A at the point of 12 hr and 1 day after surgery and peak CPK level was also significantly lower (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)