Failed bypasses are uncommon, especially in the hands of an experienced surgeon. Still, it happens often enough that agencies keep track of such setbacks as a way to grade hospitals.
Don't assume that you're guaranteed good results just because your hospital performs lots of operations. A 2004 study found that sheer volume doesn't matter much when it comes to bypass surgery. The veritable bypass factories might be somewhat safer for patients over 65, but a big difference has not been shown.
No matter which hospital you choose, bypass surgery always comes with risks. About 2% of patients die in the hospital or within one month of the operation. A study in 2001 found that about one in four patients developed cognitive problems that remained evident six months after the operation. Another recent study found that more than 7% of all bypass patients experience acute kidney failure.