What is the difference between a Cardiac nurse and a Cardiac nurse practitioner?

A cardiac nurse is a registered nurse in the field of cardiac care (ie the cardiac floor of a hospital) treating and caring for patients under the direction of a doctor.

A Cardiac Nurse Practitioner (depending upon the state) may or may not work under a doctor but has their RN in addition to a more advanced nursing license and can often diagnose heart conditions and prescribe medications.