Best Cardiac Surgeon in Pune Coronary Heart disease occurs when the blood vessels that provide blood and oxygen for the heart muscle become narrow and hard. This is often called “hardening of the arteries.Hardening occurs when fatty material forms a plaque on the walls of the coronary arteries. This plaque narrows the arteries, making it difficult for blood to get through. When blood can’t flow properly to the heart, a heart attack may occur. Open-heart surgery is also done to: repair or replace heart valves, which allow blood to travel through the heart repair damaged or abnormal areas of the heart implant medical devices that help the heart beat properly replace a damaged heart with a donated heart (heart transplantation)