Moxaprindine, a new anti-arrhythmic drug, with characteristics similar to aprindine, has been demonstrated to be highly effective in suppressing ventricular arrhythmias occurring before, during and after maximal exercise stress testing. This effect was obtained both in subjects with clinically normal hearts and in a limited number of patients with ischemic heart disease. These findings demonstrate the efficacy and safety of anti-arrhythmic treatment by drugs prolonging ventricular depolarization for ventricular arrhythmias occurring during exercise.