Heart surgery. Image 1 of 24. Surgeon using a cautery knife to open a patient's chest during heart surgery. He is also using a metal retractor to pull back the skin to allow easier access. A scalpel would have been used to make the initial incision. A cautery knife is used to make the deeper incision because it burns (cauterises) the skin and flesh to prevent bleeding. This chest is being opened to perform heart valve replacement surgery. For a sequence showing the operation, see images M560/494 to M560/517.