Pseudoaneurysm of the mitral-aortic intervalvular fibrosa (MAIVF-P) is one of the rare complications of endocarditis or, more rarely, of surgical trauma. This condition is characterized by a pseudoaneurysm in the intra-annular area between the mitral valve and the aortic valve communicating with the outflow tract of the left ventricle, between the coronary or noncoronary left aortic valve and the front flap of the mitral valve. Nowadays, surgery is recommended to avoid further growth and complications. We hereby describe the case of a patient with MAIVF-P as a consequence of a surgical trauma and early appearance of MAIVF-P. During the long echocardiographic and clinical follow-up, the patients showed stable clinical and hemodynamic conditions despite the increase in size of the MAIVF-P. A conservative treatment based on a medical follow-up can represent an alternative in patients refusing surgery, in high-risk surgical patients as well as in patients showing a stable echocardiographic and clinical picture regardless of the MAIVF-P size.