Abstract Background Pseudoaneurysm (PSA) of the left ventricle (LV) is a rare periannular complication of infective endocarditis (IE) and it is associated with high risk of free wall rupture. The diagnosis is challenging because the exact incidence and the pathogenesis is still unclear. Case summary A 69-year-old lady underwent prosthetic mitral valve replacement (MVR) for infective endocarditis secondary to Staphylococcus Aureus sepsis complicated by multiple embolizations. In the post-operative period the patient developed persistent low grade fever with negative blood culture. Transesophageal echocardiography (TOE) revealed complete posterior valve detachment and a pseudoaneurysm sac arising from antero-lateral commissure; the color flow Doppler showed massive mitral regurgitation. Thoracic CT scan confirmed the echo data and the exact localization of the cardiac rupture. The patient underwent reoperation, a pericardial patch was sutured to exclude the Pseudoaneurysm sac, and a mechanical prosthesis valve was finally implanted. A follow-up TOE revealed the exclusion of the pseudoaneurysm; two leakages with mild perivalvular mitral regurgitation were found, with no hemodynamic impact. Discussion In our case the patient developed a pseudoaneurysm of the left ventricle as a consequence of periannular extension of infective endocarditis on the mitral valve. PSA is a potentially lethal complication, if not promptly treated. Multimodality imaging including echocardiography and CT scan is recommended, in order to plan surgery ad hoc.