Manhattan Cardiology is an excellent practice (at least from the cardiology end—I have not used the gastroenterology dept)
My main reason for saying this is the absolutely wonderful Dr Beniaminovitz and his PA Kristi Loehr. They answer all your questions and never make you feel rushed. The exams are comprehensive and they give you the results.
Dr B (that last name!) is not only extremely intelligent, but also very compassionate; you feel that he really cares about his patients.
The front desk is very pleasant too (although sometimes there is a wait).
All in all, highly recommended.