At the time of preoperative coronary angiography in 44 patients left ventricular angiograms immediately after high frequency stimulation and after administration of nitroglycerin were performed. For interpretation we used the shortening (in percentage) of 8 vertical semi-diameters and of longitudinal axis in biplane angiograms. The data found in 15 healthy persons were used for comparison. Looking at the rate of shortening after high frequency stimulation myocardial areas endangered by hypoxia could be unmasked. By giving nitroglycerin thereafter we were able to differentiate between reversibly and irreversibly damaged areas. In 7 patients this has already been proven by postoperative examination. In preoperatively reversibly damaged myocardial areas no hypokinesis could be observed any more after successful revascularization. In contrast there was no improvement seen in preoperatively irreversibly damaged areas in spite of graft patency. The described preoperative angiography-test allows: 1. to unmask myocardial areas endangered by hypoxia. 2. to differentiate preoperatively between reversibly and irreversibly damaged areas. 3. more precise indication as well as better control of the results of revascularization.