We report the case of a patient with streptococcal mitral endocarditis discovered following an ischaemic cerebrovascular accident. The clinical evolution was marked by the progressive development of a mycotic aneurysm. Surveillance was performed with repeated angio-MRI which provided an indication for embolisation. We demonstrate the value and the current quality of angio-MRI for the diagnosis of mycotic aneurysms, and the value of active management of these lesions which present a high risk of rupture and which are associated with a significant excess mortality. Embolisation can allow earlier cardiac surgery for haemodynamically unstable patients and for those whose neurological state until now contra-indicated intervention.