A prospective long-term follow-up study is reported of 18 of 19 patients who survived a bout of presumed myocarditis 6-136 months (average 54 months) previously. The study included 14 males and four females, ranging from 27 to 63 years of age (mean, 44 years). Chest X-ray, ECG, echocardiogram, and resting and exercise radionuclide ventricular ejection fraction (RNVEF) for assessment of ventricular function were evaluated at follow-up. Resting and exercise RNVEF from seven control subjects were evaluated for comparison. Residual abnormalities were noted in chest X-ray (16%), echocardiogram (30%), and ECG (55%) in these predominantly asymptomatic patients (17/18 or 95%). The resting RNVEF (mean +/- SD) for the myocarditis group versus controls were 0.57 +/- 0.1 and 0.65 +/- 0.1 (P = NS), respectively. The exercise RNVED for the myocarditis group versus controls were 0.56 +/- 0.1 and 0.74 +/- 0.05 (P less than 0.01), respectively. Abnormal resting RNVEF was noted in six (33%) and exercise RNVEF in 14 (77%) patients in the myocarditis group. Two patients with abnormal exercise RNVEF subsequently developed findings consistent with dilated cardiomyopathy. It is unclear as to whether the abnormal ventricular function may serve as a marker for future development of dilated cardiomyopathy.