Cardiac glycosides may cause in the exercise ECG of healthy persons S-T segment depressions, which imitate a coronary insufficiency. If this method of examination is to be carried out in diagnosing coronary heart disease, it is - therefore - recommended in many cases to discontinue, at all events, an eventual digitals therapy before the examination in order to avoid falsely positive results. 23 healthy men (average age 30.2 years) were applied digoxin of medially quick saturation over seven days. Exertion electrocardiograms at the bicycle ergometer were registered before and after digoxin application. In five further cases, plasma glycoside concentrations were evaluated by 86Rb erythrocyte assay; upon the degree of saturation used, these concentrations - on the sixth and seventh day - amounted to x = 1.03 ng/ml. The following items manifested after digoxin administration, under stress and after resting: Retardation of heart rate, declination of T amplitude, and individually to a very different extent - depression of the S-T segment. After application of digoxin, only 8 of the 23 test persons demonstrated S-T depressions that would have corresponded entirely to the conditions of a "coronary insufficiency". Thus, it appears to be justified to carry out - first of all and in order to exclude the possibility of a coronary insufficiency - an exertion electrocardiogram, without interruption of the glycoside therapy, also in patients who are undergoing a digitalis therapy. The reason for this measure is the fact that in healthy persons only one third of the cases must be expected to show a falsely positive result. If, however, significant S-T depressions occur, the examination has to be repeated after a sufficiently long-lasting glycoside-free interval.