You need to first of all pass your that is graduate the MBBS degree then apply for the NEET POST GRADUATION EXAMINATION AND depending upon it's merit score, you'll get an admission for posting graduation course. You need to select the cardiology course to become a cardiologist.

Refer to the website below to know more about the same..

https://www.careers360.com/courses/cardiology-and-thoracic-science-course

Best wishes. Thank-you.