First of all -- never bother the Doctor with questions! Doctors aren't there to talk to you -- they're there to do to you.
If he's anything like me, your Doctor has a million other things to worry about, like how to hide an erection under the lab coat, how to get re-certified after those nurses ratted him out, and where his perscription pad ran off to.
Time spent gabbing with you is valuable time they could be billing to another patient's HMO, or to your HMO, or perhaps both simultaneously if the damn nurses won't rat them out. And that Porsche don't pay for itself! So leave your Doctor be. Answering your questions is what I'm here for.
Now, the heart bypass operation is a tricky little devil. Basically, here's what happened: due to bad living, your grandpa's heart has become diseased. My own research has shown that this condition can develop through years of whoring, drinking, "poppers," fisting, rimming, and eating red meat. Yes, although it's not pleasant to think on it, your grandpa has definitely done each of these things at least once in life, perhaps more times if he enjoyed it, and I'm sure he did, because who wouldn't? I hope your grandma has already passed, else she may yet die from the shame of it all.
So gramps has a diseased heart. What now? We bypass that sick ol' ticker. Using veins taken from the thigh, supplanted with aquarium tubing, we re-route all of the major veins and arteries around the heart, avoiding all of the sickness it contains. The heart will wither and die, taking the sickness with it.
The more astute reader will ask -- what about the thigh? If you take a vein from the upper leg, how will it function? Well, it won't. You may have noticed that right now gramps is lying in a hospital bed. Get used to it.
Put his medical degree to use for you! Send your medical question to Dr. Joe!