Dynamic cardiomyoplasty has been reported in the treatment of severe myocardial failure. In this investigation significant improvement of left ventricular function with dynamic cardiomyoplasty was demonstrated in patients with dilated cardiomyopathy or Chagas' disease for more than 1 year of follow-up. Thirteen patients with advanced heart failure who were in New York Heart Association class III or IV were operated on. There were no operative deaths. Patients were followed up for a mean of 11.5 months, and two patients died during the late follow-up period. Five of nine patients observed long term are in New York Heart Association class I, three in class II, and one in class III. At 3 months of follow-up, Doppler echocardiography demonstrated that left ventricular segmental wall shortening increased from 11.4% +/- 2.3% to 16.4% +/- 3.9% (p less than 0.01), and left ventricular stroke volume from 23.9 +/- 5.7 to 34.4 +/- 10 ml (p less than 0.01). Radioisotopic left ventricular ejection fraction improved from 20.9% +/- 3.3% to 25.4% +/- 7.7% (p = 0.06), and its better increases occurred in patients with lesser left ventricular end-diastolic dimensions. Cardiac catheterization showed that left ventricular stroke work index increased from 14.6 +/- 3.8 to 23.7 +/- 6.7 gm.m/m2 (p less than 0.01), whereas pulmonary wedge pressure decreased from 24.8 +/- 3.7 to 17.2 +/- 5.8 mm Hg (p less than 0.01). At 6 and 12 months of follow-up, all the preceding values remained essentially unchanged. Thus cardiomyoplasty improves left ventricular function and may halt the steady evolution of severe cardiomyopathies.