Tricuspid regurgitation due to rupture of a chorda is a rare disease in newborns. Recently, we experienced one day old male with tricuspid regurgitation due to rupture of a chorda of anterior papillary muscle, and who had suffered from severe hypoxemia, acidosis, cyanosis, and bradycardia. Preoperative diagnosis was pulmonary atresia with intact ventricular s ptum, massive tricuspid regurgitation, and patent ductus arteriosus by echocardiogram, which demonstrated no flow through the pulmonic valve. At operation, the pulmonic valve was intact and a chorda of anterior papillary muscle was ruptured. Tricuspid regurgitation was corrected successfully with reconstruction of the chords. Postoperative course was complicated by pneumonia and sepsis, but the infant recovered and discharged at postoperative 20 days.