We experienced a rare case of traumatic ventricular septal defect by penetrating stab injury The patient was 26-year-old women who got stab wound at the left anterior third intercostal space and left sternal border with a knife. seven hours after admission, the patient was undertaken an emergency thoracotomy due to hypovolemic shock caused by massive bleeding from transected left internal mammary artery, vein, and right ventricular outflow tract. On postoperative second day, the patient was suffered from moderate dyspnea, and arterial blood gas analysis and chest X-ray revealed hypoxemia and pulmonary edema. Right heart cardiac catheterization with Swan-Ganz Cathater showed oxygen step-up between right atrium and main pulmonary artery and a 1.6:1 ratio of pulmonary to systemic blood flow. At operation, harsh systolic thrill was palpable along right ventricular outflow tract. Through small vertical right ventriculotomy, the linear ventricular septal laceration on infundibular septum was noticed, and its size was 1.5cm with sharp margin This defeat was repaired by three interrupted matress sutures using Prolene 4-O with pledget. Her postoperative course was uneventful, and she discharged with good physical condition.