The technique of prosthetic mitral valve (MV) implantation via atrial septotomy, with retention of all portions of anterior and posterior leaflets and chordae is illiustrated. The anterior leaflet is detached from its annular attachment and is divided in two halves retaining all leaflet tissue and chordae. These are retracted and sutured separtely onto the mitral valve annulus, at 4 and 8 o'clock positions by valve sutures. Posterior valve sutures incorporate and exclude from the mitral valve orifice the posterior leaflet and its chordae. Prosthetic leaflets must be carefully examined for freedom of motion. Fifty-five consecutive isolated valve operations using this technique resulted in no mortality and excellent ventricular function.