A technique to intraoperatively assess mitral valve function after reconstruction is described. Cold cardioplegic solution is infused into the left ventricle at low intraventricular pressure (less than 15 mm-Hg) via the cardioplegia infusion line. The infusion of a crystalloid solution, instead of blood, clearly demonstrates residual leaks. Additional pump lines are not required and hypothermic cardioplegic arrest is maintained, thus allowing for repeated testing and additional repair. In combined aortic and mitral valve procedures, a Foley catheter is used to seal the aortic annulus and to infuse the crystalloid solution into the left ventricle. This method has been found to simplify mitral valve testing after reconstruction in a series of 25 patients since September 1979. Testing prompted additional repair in 4 patients and subsequent valve replacement in 2 patients.