This prospective, randomised, doubleβblind, controlled clinical study was performed at a single tertiary referral centre to test the hypothesis that the prophylactic administration of amrinone before separation of a patient from cardiopulmonary bypass decreases the incidence of failure to wean, and to identify those patients who could be predicted to benefit from such preβemptive management. Two hundred and thirtyβfour patients, scheduled to undergo elective cardiac surgery, were randomly allocated to receive either a bolus dose of 1.5βmg.kg^β1^ amrinone over 15βmin, followed by an infusion of 10β__Β΅__g.kg^β1^.min^β1^, or a bolus of placebo of equal volume followed by an infusion of placebo. Treatment with amrinone or placebo was initiated upon release of the aortic crossβclamp, before weaning from cardiopulmonary bypass. Anaesthetic technique, monitoring and myocardial preservation methods were standardised for both groups. Significantly fewer patients failed to wean in the group that received prophylactic amrinone than in the control group (7 vs. 21%, pβ=β0.002). Amrinone improved weaning success regardless of left ventricular ejection fraction, although this benefit was statistically significant only in the group with left ventricular ejection fractions >β55%. Of the 32 patients who failed to wean from cardiopulmonary bypass, 14 had normal preβoperative left ventricular ejection fractions.