Hi,
To become a cardiologist, get the admission in PG course leading to Doctor of Medicine (MD) in general medicine. After finishing 3 year degree of MD, go for the super specialty course of 3-year DM in Cardiology to be a Cardiologist.
Salary of a cardiologists depends upon several factors that includes experience, sub specialty, location, ability and the type of hospital you are working for. Salary in government hospital is different from private one. In private sector, a cardiologist can expect an average monthly salary of Rs 1 lac. A reputed cardiology surgeon earns the salary of around 1.5 lacs.

So it depends largely.

Good luck.