What is the Medical term meaning heart?

Cardiac is the medical term usually used when referring to the heart. When joined as a combining form with another suffix or word to form another term, cardiac becomes Cardio-. For example, Cardiovascular.

Cardio- = heart and vascular = blood vessels.

Cor is another word that is Latin for heart. It is used in medicine to refer to the heart. For example, Cor pulmonale (a severe condition of the heart). Another term from the Latin root is Coronary, which also means heart. For example, Coronary Artery Bypass Graft, AKA CABG (called also "cabbage"), is the medical term for a "heart bypass".

Cardiac means pertaining to the heart. Cardia means heart but isn't used by itself often.