Hi and welcome to Healthcaremagic. Thank you for your query. Blood clot usually develops as a consequence of atrial fibrillation or some other heart rythm disorder. ALso, some coagulation disorders may predispose as well. It is important to take anticoagulants now until clot is dissolved and later you can search for exact causes. Previous surgery is something that could have led to this but also clots legs as a part of deep vein thrombosis or in some other parts may have travelled to heart. I am sure that this will be treated properly. LAter you may need antiaritmic medications. I hope I have answered you query. If you have any further questions you can contact us in every time.