Coronary angiograms and treadmill stress tests were reviewed in 89 patients. Changes in R wave amplitude were measured in the control and immediate postexercise periods. Of 45 patients with normal coronary arteries, 41 (91 percent) had a decrease in R wave amplitude (P less than 0.01); 3 (7 percent) had an increase in amplitude, including 2 with abnormal left ventriculograms. The remaining patient (2 percent) had abnormal wall motion but no change in R wave amplitude. Among the 44 patients with significant coronary artery disease (70 percent or greater luminal narrowing in one or more vessels), R wave amplitude increased after exercise in 26 (59 percent) with more severe coronary artery disease. R wave amplitude decreased in 18 patients (41 percent) with normal or minimally abnormal resting ventriculograms and less severe coronary artery disease (P less than 0.01). Changes in R wave amplitude reflect ventricular function, an increase in R wave amplitude reflecting more severe dysfunction and severe coronary narrowing. A decreased R wave amplitude indicates normal or minimal dysfunction and is strongly associated with normal coronary angiograms.