Pulmonary function data, including diffusing capacity, were evaluated in 56 patients with chronic severe cardiomyopathy before heart transplantation. Cardiac catheterization data were used to describe the relationship between cardiac and pulmonary function. Of 56 patients 44 had some abnormality in pulmonary function. The majority, 30 of 56, had a restrictive impairment alone. Of 28 patients in whom diffusing capacity was measured, 64% had a diffusion impairment. There was no association of pulmonary function impairment with type of cardiomyopathy or smoking history. Pulmonary capillary wedge pressure correlated positively with Dco_CO, but not with FVC or TLC. Cardiac index and ejection fraction did not correlate with diffusing capacity. This precardiac transplantation cardiomyopathy patient group demonstrated frequent pulmonary function abnormalities not previously recognized.