Fourty-three patients undergoing open heart surgery were subjected to extended hemodynamic and metabolic monitoring (arterial and coronary sinus (CS) lactate concentration). In 95% of patients investigated, a significant increase in CS lactate concentration above the arterial lactate concentration was established at the beginning of reperfusion (RPT). In these cases, a decrease in the CS lactate below the arterial concentration occurs within the RPT creating a cross-over point (COP) from negative to positive lactate extraction values. Whereas the initial rise in CS lactate is an expression of the expected ischemia-induced acceleration of anaerobic glycolysis, the onset of a positive lactate extraction can be related to reconsolidation of mitrochondrial oxidative phosphorylation. We found two groups with an early and late COP at 7.2 +/- 0.8 min (ECOP) and 42.5 +/- 5.2 min (LCOP) (P less than 0.005). Whereas a short cross-over time was associated with a normal postoperative outcome, cardiac recovery was delayed in the LCOP group. With the aid of metabolic monitoring it is possible to identify the COP and cardiac overload situations and so to optimize the perioperative outcome, especially in selected patients (NYHA stage III/IV, re-operation, high-risk operation).