Hey Prajwal !
MBBS is the most basic course which an aspiring doctor has to complete in order to be at a position in front of people.
There's no particular choice available in MBBS unlike that of B.Tech.
Every Candidate who cracks NEET UG, and enters in a medical college is entitled to the same course of MBBS.
In order to be a Cardiologist, you have to follow quite a many steps friend.

1. Crack NEET UG
2. Crack NEET PG and get a clinical branch under General Med. or Surgery.
3. Crack NEET Superspeciality and then go for Cardiology.

This isn't a easy path, buddy.
NEET UG was the most easiest of the exams in this line. What lies in front is quite difficult.

Hope this helps.

All the Best !