The mitro-aortic intervalvular fibrosa (MAIF) connects the anterior mitral leaflet to the posterior portion of the aortic annulus. The aneurysms of MAIF represent a complication of aortic valve endocarditis, but blunt chest trauma, aortic valve replacement and congenital heart disease have also been reported as a cause. We describe a case of an aneurysm of MAIF, whose progression was documented by serial echocardiographic observations. To the best of our knowledge, this very rare occurrence has not been reported previously.