We present a case of an isolated large ventricular septal defect (VSD) following blunt chest trauma in a motor vehicle accident in the patient with preexisting mechanical mitral valve. Transthoracic echocardiography revealed a large muscular VSD with significant left to right shunt along with septal edema. Surgical repair was performed in view of Qp:Qs of 2.5 with significant hemodynamic instability despite intra-aortic balloon pump. The ventricular septal defect was found in apical muscular portion of the interventricular septum, which was closed through left ventriculotomy. We here discuss the possible mechanisms of damage and importance of timely surgery. To conclude, minor looking external injury might contain devastating damage inside, especially with patients on anti-coagulant therapy.