OBJECTIVE This study sought to assess the short-term effect of discontinuing latissimus dorsi muscle stimulation on left ventricular systolic and diastolic performance and exercise tolerance in patients with improved functional status by cardiomyoplasty, in whom latissimus dorsi muscle was fully conditioned. BACKGROUND Cardiomyoplasty has consistently improved the functional status of patients, but the short-term effect of latissimus dorsi muscle contraction has not been assessed in these patients. METHODS Right-heart catheterization, Doppler-echocardiography and maximal exercise testing with expired gas analysis were performed in 10 patients with congestive heart failure who had undergone cardiomyoplasty at least 6 months earlier. Data were obtained when the latissimus dorsi muscle was stimulated every other systole and after stimulation was discontinued for 1 h. The power of this study to detect a 10% difference was > 80%. RESULTS After cardiomyoplasty, left ventricular ejection fraction increased from 0.22 +/- 0.08 (mean +/- SD) to 0.27 +/- 0.07 after 6 months (p < 0.02 vs. before cardiomyoplasty) and to 0.24 +/- 0.09 after 1 year; functional class went from 3.0 +/- 0.0 to 2.0 +/- 0.5 after 6 months and to 2.0 +/- 0.7 after 1 year (both p < 0.001 vs. before cardiomyoplasty). After discontinuation of latissimus dorsi muscle stimulation, cardiac index did not change (2.28 +/- 0.45 vs. 2.30 +/- 0.46 liters/min per m2). Mean systemic arterial and pulmonary capillary wedge pressures were also similar (85.2 +/- 6.0 vs. 88.4 +/- 5.6 mm Hg and 14.9 +/- 7.1 vs. 13.6 +/- 6.8 mm Hg, respectively). Doppler E/A ratio decreased from 1.04 +/- 0.33 to 0.83 +/- 0.25 (p < 0.02), suggesting that left ventricular diastolic function may have been improved by latissimus dorsi muscle stimulation. Peak oxygen consumption was unaltered (1,633 +/- 530 vs. 1,596 +/- 396 ml/min). CONCLUSIONS Alterations in left ventricular diastolic rather than systolic function may be responsible for the long-term clinical benefits of cardiomyoplasty.