Introduction: Inspite of demonstrable gratifying clinical results, the mechanism of transmyocardial laser revascularization (TMLR) has not been clarified reliably to date. In order to examine whether TMLR leads to an amelioration of myocardial tissue oxygenation it is possible to determine the partial oxygen tension (pO 2 ) in the myocardium directly via a special pO 2 -measurement catheter. An increase of myocardial partial oxygen tension would be an additional indication for an immediate amelioration of oxygen supply in the ischemic heart by TMLR.Materials and methods: In six patients receiving TMLR treatment, specially designed pO 2 -measurement probes were placed in the ischemic myocardium. In this area, laser treatment was performed subsequently (1 channel/cm 2 , energy: 40 J, 800 W CO 2 -Laser). Myocardial partial oxygen tension was determined via online measurement (transcutaneous conduction) before, during and up to 3 days after the operation. The principle of measurement is based on a chemical reaction taking place at a polarographic electrode and generating a measurable flow of electrons. Parameters which are affecting the pO 2 such as hemodynamic and respiratory parameters, medications, as well as hemoglobin and hematocrit, were documented simultaneously.Results: In the ischemic heart muscle tissue pO 2 values between 4 and 20 mmHg were found before TMLR. In all patients, an increase of myocardial partial oxygen tension up to 20 to 50 mmHg was verifiable in the measurement period. It was demonstrated that the parameters mentioned above do not affect intramyocardial pO 2 significantly in the post-operative phase. All patients revealed an amelioration of their clinical symptomatology postoperatively. In comparison to their preoperative status (all patients had CCS-classification IV), all patients were free of medical complaints on ward level in the early postoperative phase.Conclusion: TMLR results in an amelioration of myocardial oxygen supply in the early postoperative phase. For the first time this direct evidence was made possible via the measurement technique described.