The aim of this study was to assess in vivo the efficacy of a new technique for remodeling the mitral valve. In 6 dogs during cardiopulmonary bypass and cardioplegic cardiac arrest, both mitral valve leaflets were totally separated from the mitral ring and resected subtotally, leaving intact their narrow margins with insertion sites of the chordae tendineae of the first and second order. To mimic pathologic conditions, the chordae tendineae were then altered by placing two shortening sutures for every chordal stem. Based on standardized geometric calculations and using autologous pericardium treated with 0.62% glutaraldehyde solution, the new leaflets were then remodeled intraoperatively and sutured in place, merging them with the subvalvular apparatus and the native mitral ring. After restoration of stable circulatory conditions, valve function was evaluated under rest and defined loading conditions using a 5.0-MHz ultrasound transducer, applied epicardially. We found that intraoperative remodeling of the mitral valve leaflets using autologous pericardium with preservation of the subvalvular apparatus is possible and reproducible, and can be performed even when the subvalvular apparatus is altered morphologically. Functionally, the remodeled valve proved to be satisfactory under conditions of rest and stress. The benefits conferred by autologous tissue, the reproducibility of the surgical technique, the good functionality of the remodeled valve, and the preservation of the subvalvular apparatus could make this technique a useful surgical alternative for extensive mitral valve reconstruction procedures in pediatric and adult patients.