A composition for use in the treatment of a pseudo aneurysm in a subject, said composition comprising: i) microbubbles； ii) a magnetic material； and iii) a blood clotting agent； said treatment comprising administering said composition directly into the pseudo aneurysm and applying a magnetic field to the pseudo aneurysm so as to retain the blood clotting agent within the pseudo aneurysm for a prolonged time period compared to a case where no magnetic field is applied to the pseudo aneurysm.
