The incidence of mitral valve aneurysm in infective endocarditis is 9-10%. However, a huge giant mitral valve aneurysm larger than 3 cm in length associated with acute mitral regurgitation is very rare. The mitral valve aneurysm can be complicated with perforation, leading to severe mitral regurgitation and congestive heart failure, pending to surgical correction. We hereby report a case of twenty-three year-old female who suffered from sudden onset of chest pain and dyspnea due to acute left ventricular failure, which was developed after the perforation of huge, hanging, giant septic aneurysm on the mitral valve. The patient underwent mitral valvuloplasty and recovered uneventfully.