Dear Ashok,

In order to become a cardiologist in AIIMS, you need to appear in AIIMS exam and qualify the exam. Then after qualifying with a suitable rank , you'll have to do 5.5 years MBBS and then 3 years of MD after that 3 years of DM (cardiology). Qualifying the exam is little difficult because there are more concept based questions but if you know each and every line of NCERT then you'll definitely get good marks.

Regards