Forty-seven patients (0.08%) from a total of 5,730 consecutive patients undergoing treadmill stress tests developed one or more episodes of ventricular tachycardia. Forty patients had heart disease, coronary artery disease being the leading cause. Rest ECG was normal in 12 patients and showed long QTc (greater than 440 msec) in 16 patients. Ventricular tachycardia was brief and self-terminating, requiring D/C cardioversion in only one patient. "Exertional hypotension" preceded ventricular tachycardia in 16 of 34 patients. There was poor correlation (r = 0.16) between the rate of ventricular tachycardia (VT) and the underlying heart rate. Only four episodes of VT were initiated by R on T premature ventricular beats. In summary, exercise-induced ventricular tachycardia 1) is a rare complication of treadmill stress test and occurs in patients with heart disease; 2) is frequently preceded by "exertional hypotension," and 3) is not related to the R on T phenomenon. The high incidence of prolonged QT may indicate a role for the automatic nervous system in its pathogenesis.