Transthoracic echocardiography (TTE) has an important role in the assessment of patients with acute penetrating chest trauma. We report the case of a 36-year-old man who sustained a stab wound to the chest. After admission, he required emergency pericardiocentesis. TTE revealed a traumatic ventricular septal defect and a defect in the anterior mitral valve leaflet. To assess whether these lesions were related to the initial stab wound or the pericardiocentesis, the transducer was positioned over the stab wound, and the lesions were shown to be in the same plane as the entry site, thus ruling out iatrogenic trauma.