All open heart surgeries are performed by connecting the patient to Heart Lung Machine. This ensures supply of oxygenated blood to patient's body and brain. The heart is rested during the course of operation so that surgeon can do repair a replacement of valve or valves. Majority of bypass operations are done on Heart Lung Machine.

Although now there is a trend towards doing bypass surgery without the use of Heart Lung Machine i.e. beating heart surgery. Membrane oxygenator heat exchanger, blood filter and cardioplegia delivery system are main components of heart lung machine.