Hey! Your field of interest is medical,So you must take biology,physics and chemistry as your core subjects after 10th.If you want you may take coaching for medical..there are many institutions like Allen and Aakash that provide good coaching for medical exams.You must Focus on Time management in exams as medical exams are objective.To become a cardiac surgeon you have to score high ranks to get admission in good colleges.The MBBS is generalized for medical students and for specialixatspe you have to give PG for medical exams where you will be given specific subjects like cardiology,radiology according to your ranks.Hope this helps you!