Heart surgery. Image 3 of 9. Surgeon opening the heart during an operation to repair an aortic aneurysm. Stitches and a replacement aortic heart valve from a previous operation can be seen. A second operation is necessary because the wall of the aorta (the largest artery that leaves the heart) has become weakened, forming a dilation known as an aneurysm. Without surgery, an aneurysm can rupture with fatal consequences. During this operation, part of the aorta will be replaced with a prosthetic vessel. For a sequence showing the operation, see images M560/461 to M560/469.