Thirty patients with angiographically documented mitral valve prolapse but without associated coronary artery disease, underwent exercise 201thallium myocardial scintigraphy. The resting ECG demonstrated ST segment abnormalities in 15 patients (50%). The exercise ECGs were abnormal in 2 patients (6.7%), normal in 4 (13.3%), and inconclusive in 24 patients (80%). Two patients (6.7%) had abnormal exercise myocardial scintigraphy (both patients had abnormal exercise ECGs). Two additional patients (6.7%) had perfusion abnormalities in the rest images that did not change with exercise. Twenty-six patients (86.4%) had normal scans. The authors conclude that the majority of patients with mitral valve prolapse have normal exercise 201thallium images in the absence of associated coronary artery disease and exercise electrocardiography is of limited value in patients with mitral valve prolapse because the results are frequently (80%) inconclusive.