The diagnosis of myocarditis is difficult and is generally one of exclusion. Moreover, endomyocardial biopsy (EMB) is not a sensitive technique. Magnetic resonance imaging (MRI), however, has shown promising results in diagnosing myocarditis. We evaluated 20 patients with a clinical suspicion of acute myocarditis. Troponin I levels were elevated in 17/20 patients. Cardiac catheterization (n = 13) showed no evidence of coronary artery disease, while normal findings were reported in all five patients who underwent EMB. MRI performed 9.8 +/- 7.5 days after the onset of symptoms showed an LV-EDV of 172 +/- 50 ml and LV-EF of 57 +/- 10%. Abnormalities on delayed contrast-enhanced MRI were found in 15/20 patients, involving 3.7 +/- 2.1 segments using the 17-segment model. The lateral LV wall was most frequently involved (61% of enhanced segments). The enhancement was most frequently subepicardial, less often transmural, or midwall (respectively, 67%, 22%, and 11% of enhanced segments). Mild to moderate systolic wall motion abnormalities were invariably found in the abnormally enhancing myocardium on MRI. Associated pericardial effusion was found in six, pericardial enhancement in nine patients. In conclusion, the present study suggests an important role for MRI in evaluating patients with clinical suspicion of acute myocarditis. Not only can the myocardial damage be precisely depicted but also concomitant involvement of the pericardium and impact on regional and global ventricular function can be assessed.