If angiotensin I converting enzyme inhibitors are now widely used in the chronic treatment of severe congestive heart failure (CHF), they are generally withdrawn during acute pulmonary edema (APE) episodes. Indeed, if they meet most of the criteria required for a drug used in this acute context, they could also induce deleterious effects on renal function and electrolytes. Objective: the purpose of the study was to evaluate both the efficacy and safety of a single intravenous 2h-infusion of 1 mg enalaprilat (E) 12 to 18h after an APE episode. Methods: this was a placebo (P) controlled, randomized and double-blind study performed in 20 CHF (III-IV NYHA) patients (11 E and 9 P). Systemic and regional hemodynamic parameters, biological parameters and blood gases were measured before and 2, 4, and 8h after the onset of treatment infusion. Results: As compared to P, E decreased pulmonary capillary wedge pressure (-37 vs -10%, p=0.001), diastolic and mean systemic (-21 vs -4%, p=0.009; -18 vs -6%, p=0.026) and pulmonary (-21 vs -8%, p=0.040; -18 vs -9%, p=0.046) arterial pressures, brachial and renal resistances (-44 vs -14%, p=0.017; -22 vs -2%, p=0.014), increased brachial and renal blood flows (+77 vs +8%, p=0.036; +12 vs 0%, p=0.043), arterial oxygen tension (+2 vs -16%, p=0.041) and saturation (+1 vs -2%, p=0.045) and finally tended to increase brachial artery diameter (+13 vs 0%, p = 0.081) and to improve intra-pulmonary shunt (-18 vs -16%, p=0.080). Simultaneously, E did not affect heart rate, cardiac output, systolic systemic and pulmonary arterial pressures, and carotid and hepato-splanchnic hemodynamics. Finally, E decreased plasma converting enzyme activity (-81 vs -30%, p=0.001), but did not change plasma renin activity, aldosterone, noradrenaline, adrenaline, vasopressin, atrial natriuretic factor, and electrolytes, creatinine and urea clearances. Conclusion: early administration of enalaprilat is effective and well-tolerated in CHF patients with APE.