Left ventricular outflow tract pseudoaneurysm is an uncommon but potentially catastrophic complication of aortic valve surgery, aortic valve endocarditis or chest trauma. We describe a case of a left ventricular outflow tract pseudoaneurysm 1 month after an aortic valve replacement that caused a systolic compression of mitral valve and a severe regurgitation. The diagnosis was confirmed using transoesophageal echocardiography, magnetic resonance image and intraoperative endoscopy. Surgical repair of the pseudoaneurysm corrected the mitral regurgitation.