This study delineates the effects of congestive heart failure on routine pulmonary function tests and assesses the changes in pulmonary function as congestive heart failure was treated. Twenty-eight patients had spirometry, lung volumes, and diffusing capacity measurements initially and at frequent intervals after their initial hospitalization for congestive heart failure. Initially the patients had both obstructive (mean forced expiratory volume in 1 s [FEV1], 48.2% +/- 13% predicted) and restrictive (mean forced vital capacity [FVC], 5.6% +/- 15.7% predicted) ventilatory dysfunction, but a normal carbon monoxide diffusing capacity. With treatment, pulmonary function rapidly improved initially and there was no further significant improvements in the mean pulmonary function after two weeks of treatment. However, there was marked interindividual variability and several patients took months to reach their best level of pulmonary function. Even with treatment, the patients retained evidence of obstructive ventilatory dysfunction and at the time of their best spirometry 53% (8/15) of nonsmokers still had an abnormally low FEV1/FVC ratio.