Penetrating cardiac injuries are life-threatening emergencies. We present a case of a 24-year-old construction worker who accidentally shot himself with a nail gun. Chest X-ray showed a 6 cm-long nail overlapping the cardiac shadow. A computed tomography (CT) scan revealed the nail penetrating the left ventricle and a large amount of pericardial effusion. Median sternotomy was performed and cardiopulmomary bypass was established. Then, the nail was removed and the left ventricular wound was repaired by 4-0 Prolene mattress sutures buttressed with felt-strips. He had an uncomplicated postoperative course and was discharged 7 days postoperatively.