Recent reports have demonstrated substantial increases in pulmonary activity during radionuclide stress exercise studies in patients with coronary heart disease. These studies have shown that the degree of the increase reflected the severity of the underlying disease. We studied the effects of supine exercise on systolic function and pulmonary activity in ten normal control subjects and 20 patients with congestive cardiomyopathy (12 ischemic and 8 idiopathic). Ejection fraction rose in the normals (P less than 0.001), end-diastolic volume increased slightly but significantly (P less than 0.05), and pulmonary activity rose by less than 16%, (mean 10%) while cardiac output increased by 162%. On the other hand, the myopathy patients demonstrated a small increase in cardiac output, (+49%) with a more substantial increase in pulmonary activity (+25%, P less than 0.05 vs normals). In these patients, ejection fraction did not change during exercise, while end-diastolic and end-systolic volumes rose. In the myopathy patients, the cause for an increase in cardiac output was a rise in heart rate, with little change in stroke volume. We conclude that pulmonary activity rises in myopathy patients to a greater extent than in normal controls. This probably reflects the greater elevation in filling pressures these patients need to maintain forward cardiac output.