1. Since important interrelationships between haemodynamic and hormone indices are possible in cardiac failure, measurements of cardiac output, mean pulmonary artery pressure, plasma renin activity, angiotensin II and aldosterone were carried out before and during acute and chronic frusemide therapy in patients with oedematous heart failure who had been given digoxin.
2. Cardiac output fell significantly 90 min after acute frusemide injection, then returned to baseline. Mean pulmonary artery pressure declined steadily throughout the 4 h of observation.
3. These haemodynamic changes occurred in the absence of major hormonal fluctuations and related presumably to direct vascular and diuretic actions of frusemide.
4. With more chronic (8–10 days) oral frusemide therapy, reciprocal changes between haemodynamic and hormone indices were observed. As the diuretic response to frusemide diminished, cardiac output and pulmonary artery pressure declined whereas the renin-angiotensin system was activated. Statistically significant inverse correlations were observed between these haemodynamic and hormone indices.
5. In both acute and chronic phases of the study, fluctuations in aldosterone levels were regulated by the renin-angiotensin system whereas ACTH, plasma potassium and plasma sodium played, at best, supportive roles.