Among 68 children with severe dilated cardiomyopathy, 43 (aged 10 months to 15 years) presented with active myocarditis, diagnosed by endomyocardial biopsy. They were divided into four treatment groups: I, controls: 9 patients submitted to conventional treatment (digitalis, diuretics, and vasodilators) for 8.1 +/- 0.7 (SD) months; II, prednisone: 12 patients received conventional therapy plus prednisone; III, azathioprine: 16 patients submitted to conventional therapy plus prednisone and azathioprine; IV, cyclosporine: 13 patients treated with conventional therapy plus prednisone and cyclosporine. Immunosuppressive therapy was maintained for a mean of 8.4 +/- 1.2 months. They were submitted to noninvasive (electrocardiogram, chest radiograph, Doppler echocardiogram, and radioisotopic scintigraphy) and invasive (hemodynamic) studies. In the control group only 2 of 9 patients showed clinical and hemodynamic improvement and 1 of 4, histologic regression of the myocarditis. Among patients submitted to conventional therapy plus prednisone, 3 of 12 presented clinical and hemodynamic improvement; 2 of 5 also showed histologic regression of inflammatory process. By contrast, patients treated with azathioprine or cyclosporine associated with prednisone had significantly better results: 13 of 16 and 10 of 13 patients, respectively, had clinical and hemodynamic improvement; all 6 patients in the azathioprine group and all 4 patients in the cyclosporine group had histologic regression of the myocarditis. Two patients in the prednisone group, one in the azathioprine group, and one in the cyclosporine group died during treatment, in cardiogenic shock. In our experience immunosuppressive therapy with azathioprine or cyclosporine associated with prednisone improves the prognosis of children with active myocarditis and severe ventricular dysfunction.