It sounds like your friend is going in for a bypass operation. In this procedure extra veins are taken from the leg (saphenous veins) and used to replace blocked arteries of the heart. An incision is made in the centre of the chest to access the heart. The blocked (atherocslerotic) arteries prevent the flow of blood reaching the heart muscle. When you do exercise, or any other activity that increases your heart rate (e.g. stress), the oxygen requirements of the heart muscle increase. In someone with blocked coronary arteries, blood flow and therefore oxygen delivery cannot meet the demands of exertion. As a result the patient experiences episodes of angina (chest pain) when exerted, and if the blockage is severe, at rest. This condition is referred to as coronary artery disease. Please note veins may be harvested from other parts of the body depending on a number of factors, however the leg is most common. The terms double and triple bypass are in reference to the number of blocked arteries that are being operated on. For example in a double bypass, two sections of artery are replaced by vein; and in a triple bypass, three sections are replaced. Bypass surgery is indicated in those with severe coronary artery disease as assessed by scans performed by Doctors and in those who do not respond/cannot have other treatment for various reasons that I will not go into here. Bypass operations are common these days and as such the rates of complications are low. Any surgical procedure has risks. These general risks include infection, deep vein thrombosis due to immobility/surgery itself, keloid scarring, anaesthetic complications and death. Precautions are taken for all of these including theatre hygiene etc. There are bypass complications such as pulmonary emboli (blood clots lodging in the lungs), stroke, and heart attack. These complications are fairly rare. Bypass surgery is the best option even in light of these rare complications and is indicated when the risk of no-treatment is greater than treatment as assessed by a Doctor. Following the surgery your friend should make an effort to change his/her lifestyle. This includes stopping smoking, drinking and avoiding fatty foods. A healthy diet and exercise should be commenced to prevent further damage to the heart arteries. Is this is not implemented he/she may run the risk of further blockage and a return of the symptoms mentioned. I hope this is clear and helps you. If you have further questions ask a Doctor in hospital when you visit your friend.