Cheney, 64, has a lengthy history of heart problems. He has had four heart attacks -- the first when he was only 37 -- quadruple bypass surgery, two artery-clearing angioplasties and an operation to implant a special pacemaker in his chest.

Spokesman Steve Schmidt said the vice president was doing well after the procedure on Saturday.

Cheney walked slowly out of George Washington University Hospital late Sunday morning with his wife, Lynne, at his side. He shook hands with doctors and then went to his motorcade without any assistance, although not at his normally brisk pace.

Cheney was under local anesthesia during the six-hour surgery.

Popliteal Aneurysms

An aneurysm is a ballooning weak spot in an artery that can eventually can burst if left untreated. Cheney's aneurysms, known as popliteal aneurysms, were discovered during his annual physical in July.

The vice president had been scheduled to have only the right knee operated on Saturday and the other later, but during the surgery his doctors decided to do both at once, Schmidt said. There were no complications.

Flexible Stent Grafts

Cheney had flexible stent grafts put in his knee arteries. During the procedure, the stent graft is threaded through a catheter inserted in the femoral artery at the groin down to the aneurysm site. Fully opened, it's like a little tube inside the artery, keeping the rushing blood from touching the weakened artery walls.

This is a newer technique for patching aneurysms, and an alternative to rerouting blood flow around the weak spot with a vein bypass.

Cheney, 64, has a lengthy history of heart problems. He has had four heart attacks -- the first when he was only 37 -- quadruple bypass surgery, two artery-clearing angioplasties and an operation to implant a special pacemaker in his chest.