We describe a case of cardiac tamponade due to pulmonary artery laceration as a late sequela in a patient who had sustained penetrating chest trauma. A 35-yr-old man presented to our emergency department complaining of pleuritic left chest pain, shortness of breath, and fever 19 days after being hospitalized for a stab wound to the left chest. During his first hospitalization, chest X-ray study, echocardiogram, and central venous pressure determination were all normal. On second presentation, he had a cardiac tamponade and underwent a median sternotomy. A pulmonary artery laceration was discovered and repaired. The postoperative course was complicated by readmission for postcardiotomy syndrome. This case demonstrates that late and unexpected complications can occur in patients with penetrating chest trauma and a normal initial evaluation.