Cardiosurgical operations were tested experimentally by means of a perioperative metabolic-energetic monitoring and by the conventional method of the hemodynamic monitoring (Swan-Ganz-catheter). By that could be shown that a perioperative monitoring by means of the arterio-coronary venous difference of the lactate level is possible. Intraoperative information about the topical metabolic-energetic condition of the myocardium is to receive as the decisive advantage of this method. An improvement of the therapy results is possible in that way by an optimum of the treatment. A metabolic recovery of the heart during the operation was substantial more favourable for the postoperative myocardial restitution than an early application of catecholamins. This method for perioperative observation should be used specially in risk operations (NYHA-stadium III-IV, reoperations, etc.).