Background: Papillary muscle rupture in the fetus and neonate is a rare event that leads to severe mitral or tricuspid insufficiency and is associated with high perinatal mortality. We undertook surgical repair of this lesion in the neonatal period and report on our midterm results. Methods: Three neonates with tricuspid insufficiency and 1 infant with mitral insufficiency, all due to papillary muscle or chordal rupture, underwent surgical repair with artificial chordal replacement and a modification of the de Vega annuloplasty technique that allowed external adjustment of the annulus size under transesophageal echocardiographic guidance after separation from cardiopulmonary bypass. Results: All patients recovered well from the operation. There have been no late deaths and no valve-related complications. On discharge, all 3 patients had evidence of trace to mild atrioventricular valve regurgitation. At a median follow-up of 33 months (range, 7 to 50; 123 patient-months), all 4 patients are growing normally. Three patients have had no change in the degree of tricuspid or mitral regurgitation. One patient required reoperation at 54 months postoperatively for acute mitral insufficiency secondary to separation of an artificial chorda from the ventricular wall. Conclusions: Surgical repair of critical neonatal tricuspid and mitral insufficiency associated with papillary muscle or chordal rupture is feasible and can result in good early and midterm results. Our modification of the De Vega annuloplasty technique with the ability to externally adjust the size of the annulus under echocardiographic guidance may improve the accuracy of the repair in the neonate.