Heart surgery. Image 1 of 9. Surgeon using a cautery knife to open a patient's chest during heart surgery. A scalpel has been used to make the initial incision. A cautery knife is used to make the deeper incision because it burns (cauterizes) the skin and flesh to prevent bleeding. This chest is being opened to perform a repair on an aortic aneurysm near the heart. For a sequence showing the operation, see images M560/461 to M560/469.