The paper presents a rare case of successful correction of an anterior mitral leaflet perforation. A 28-years old patient was referred with progressive heart failure symptoms at 18 weeks after he had a penetrating stab wound of the right ventricle. Massive pericardial effusion with cardiac tamponade risk and severe mitral valve insufficiency were found at examination. By the time of referral, spontaneous closure of the ventricular septal defect, which is an inevitable component of the “unhappy triad”, had happened. Accurate topical ultrasound diagnosis of the intracardial lesion that resulted from the penetrating wound of the left ventricular outflow allowed for a successful urgent mitral valve reconstruction with a xenopericardial patch and the insertion of a 28 mm MedEng annuloplasty band. To prevent any future pericardial constriction, subtotal pericardectomy by Cooley was performed.Conclusion: Perioperative echocardiography and subsequent follow up by cardiologist are obligatory in all cases of precordial wounds after discharge from hospital. Timely surgery for traumatic mitral leaflet perforation allows for a successful valvuloplasty.