Introduction: Submitral left ventricular aneurysm is a rare but well recognized entity. The aneurysm can attain a large size often distorting and compressing left atrium and left ventricle from behind. The aneurysm may develop as a complication of myocardial infarction, trauma, previous operation or infection. Mitral regurgitation is a common association. Case Report: The patient Mr. Gollo Tado, a 23 years old male from Arunachal Pradesh was admitted to GNRC Heart Institute, Guwahati with history of palpitation and dyspnoea on exertion, which was more on walking since last four years. Following an accident in 1997 he had chest pain, cough and haemopatysis which were the initial symptoms. The patient is nonalcholic, normotensive, non-diabetic and non-vegetarian. On examination his cardiovascular system revealed hyperdynamic precordium, epigastrric pulsation present. Apex beat was present in 7th inter costal space lateral to anterior axillary line. SI soft S2 normal, early diastolic murmur in 4th left parasternal area, systolic murmur at apex. No focal neurological deficit. Bio-chemical parameters were within normal limit. Chest X-ray showed cardiomegaly, Echocardiography revealed moderate AR, mild Mr. A large cystic mass posterior to heart, pushing it anteriorly compressing the left atrium and distorting the mitral valve—Submitral Aneurysm (Fig. 1). Coronary angiography-coronaries normal, LV angio–mild mitral regurgitation. There is opacification of another chamber behind LA with calcification of its wall—Submitral Aneurysm LVEF-30%. Severe aortic regugitation (Fig. 2). He was taken for operation on 1st November, 2000. Standard Cardiopulmonary bypass was instituted to him with successful delivery of aortic root cardioplegia. Left atrium was opened and the neck of the aneurysm was found calcified along with annulus of the mitral valve and the wall of the aneurysmal in places. Mitral valve was excised and blood was sucked out from the aneurysmal cavity and mouth was closed with dacron patch and mitral valve replacement was done with 27 mm on - X valve (fig. 3, 4, 5 & 6). Meticulous deairing and haemostasis were done before come off bypass. Post-operatively had several episodes of ventricular arthythmias, which were controlled by injection xylocard. After satisfactory recovery he was discharged on 12th post-operative day. Discussions: Our patient possibly developed the aneurysm following trauma. The patient became symptomatic following trauma to the chest sustained 3 years back while lifting a heavy log of wood. Presence of heavy calcification on the wall of the aneurysm may also suggest its traumatic origin. The aneurysm was very large (size 10.8 cm) compressing the left atrium and the left ventricle from behind. Coronary arteries were normal but left ventricle was with severe dysfunction. Severe aortic regurgitation was an unusual associated finding in our case. In a few reported cases of repair of Submitral Aneurysm, mitral valve was preserved while in others the mitral valve was replaced with a prosthetic valve to facilitate the repair of the aneurysm. In our case, because of the encroachment of the subvalvular apparattus by the aneurysm, excision of the mitral valve became essential.