What is the difference between a cardiologist and a cardiac surgeon? Both specialties are involved in managing patients with heart problems, but they do very different things. A cardiologist diagnoses and treats conditions of the heart and blood vessels usually with medication and sometimes with minimally invasive techniques like angioplasty. Some conditions cannot be dealt with in this way and this is when a cardiac surgeon steps in. A cardiac surgeon often performs major surgery where the patient is given a general anesthetic and their chest is opened up to access the heart. Cardiac surgeons do operations like valve replacements and coronary artery bypass grafting.