To clarify the contribution of afterload to left ventricular performance after repair of mitral regurgitation, we evaluated echocardiographically 8 children who had undergone surgical repair for isolated congenital mitral regurgitation. We examined the relationship between left ventricular systolic function and preload, afterload, and contractility. The left ventricular systolic function was strongly correlated with the afterload after the surgical repair. In the postoperative state, reducing afterload by vasodilators could be a useful means of treating cardiac failure, in addition to using catecholamines to increase the contractility.