The effect of digoxin on the right and left ventricular ejection fractions in 15 patients with pulmonary heart disease caused by severe chronic airflow obstruction was studied in a double-blind, randomized, placebo-controlled trial. All patients were ambulatory and had clinical features of right but not left ventricular dysfunction. Equilibrium radionuclide angiography showed reduced right ventricular ejection fraction in all patients and reduced left ventricular ejection fraction in four. After 8 weeks of digoxin treatment, the abnormal left ventricular ejection fractions were normal; right ventricular ejection fractions increased only in those patients who had had abnormal left ventricular ejection fractions. We conclude that in patients with pulmonary heart disease, the right ventricular ejection fraction is abnormal and improves with digoxin treatment only when the left ventricular ejection fraction also is initially abnormal.