Canrenoate (Soldactone)--a spironolactone metabolite for intravenous use--has recently been suggested as a specific antidote in patients suffering from digitalis intoxication. Theoretically, this would imply that canrenoate could counteract the effect of digoxin. The influence of canrenoate on inotropy in 12 digitalized patients was investigated by measurement of sytolic time intervals. Canrenoate improved the left ventricular contractility, since both preejection period (PEP) and the ratio between PEP and left ventricular ejection time (PEP/LVET) decreased significantly. The maximal changes in controlled atrial fibrillation, canrenoate had no effect on ventricular rate, whereas atropine increased the ventricular rate significantly.