Five patients were studied 5-13 months after dynamic cardiomyoplasty for refractory heart failure. In two, muscle flap stimulation caused a pronounced increase in cardiac index (mean 55%) and ejection fraction (mean 75%); no patient showed improvement in cardiac filling pressure. 2 years after surgery, one of the patients with haemodynamic improvement died from ventricular fibrillation, and histochemistry of the stimulated muscle flap revealed predominantly fatigue-resistant type I fibres, without evidence of fibrosis. In selected cases, dynamic cardiomyopathy could be of long-term benefit.