To evaluate the effectiveness of retrograde cardioplegia and reperfusion, a total of 266 patients undergoing coronary bypass surgery between Nov 1987 to Dec 1989 were divided into three groups depending on the method of cardioplegic fluid delivery and reperfusion. In group I (80 patients) antegrade cardioplegia and reperfusion was used. In group II (98 patients) antegrade and retrograde cardioplegia and antegrade reperfusion was used while in group III antegrade and retrograde cardioplegia and retrograde reperfusion was used. Myocardial functions were studied with the help of an on-line computer on the basis of mathematical model of heart before and after cardiopulmonary bypass. Biopsy specimens were collected before, during and after cardiopulmonary bypass in order to study myocardial structural changes. In group I patients there was decrease in myocardial function in the immediate post perfusion period while group II patients had considerable improvement in their myocardial function and groups III patients showed further improvement in it. Ultrastructural myocardial study revealed considerable detrimental changes in group I, minimal changes in group II and no change in group III patients. Thus in our experience retrograde cardioplegia and retrograde reperfusion with warm oxygenated blood provide maximum myocardial protection in patients with multiple coronary artery lesions.