Post-ischemic reperfusion phenomenon has been studied in two methods of myocardial protection: a crystalloid cardioplegia (St Thomas no.2) and a cold blood cardioplegia (Buckberg) during cardiopulmonary bypass for myocardial revascularisation in patients. Myocardial protection has been assessed from the evolution of hemodynamic parameters, reperfusion arrhythmias and biochemical analysis of the coronary flow after cross-clamp removal: creatinine phosphokinase (CPK_MB) and nucleotide adenine metabolites (adenosine, inosine, hypoxanthine, xanthine and uric acid). The study was performed in two groups of 14 patients. Hemodynamic conditions were similar in both groups during reperfusion in order to avoid different coronary flow. In those conditions, myocardial protection by cold blood cardioplegia reduced reperfusion arrhythmias, and resulted in a loss of CPK-MB release. Furthermore, the reduction of metabolites release, purine bases and oxypurine bases into coronary sinus after cold blood cardioplegia suggest a better protection of myocardial high energy phosphates in this group than after crystalloid cardioplegia. Our results also show that hypoxanthine is probably the final product of ATP degradation in human myocardial tissue.