Objective:Myocardial lactate production is regarded as a reliable sign of myocardial ischemia. In the early postoperative period after cardiac surgical intervention it consists of a combination of continued anaerobic metabolism at the beginning of postischemic reperfusion and wash out of accumulated end products of anaerobic glycolysis during cross clamping time (CCT). The prolonged deficit of myocardial metabolism during the vulnerable time of early reperfusion can cause a low cardiac output syndrome. Methods: In a prospective study of 37 patients undergoing cardiac surgical intervention with normal left ventricular function, we measured simultaneously the kinetic of lactate in both the coronary sinus and arterial blood. Haemodynamic monitoring was undertaken throughout the perioperative period by the use of Swan-Ganz catheterisation. Results: During reperfusion after CCT we assessed the cross over point from production of lactate to consumtion in the coronary sinus. In 27 patients (ECOP) a early cross over point (COT = 10,2 min) and in 10 patients (LCOP) a late cross over point (COT = 31,5 min) were found. Those patients requiring high volumes of catecholamines postoperatively were found to be in LCOP group. Conclusion: The measurement of lactate in the coronary sinus and arterial blood can be used as an instrument for the determination of catecholamine requirement and as a factor in postoperative outcome.