There were studies that were done that "proved prayer worked" they have long since been debunked due to improper use of the scientific method.

I have heard that there is some evidence that it is the other way round. Especially when people are informed that they are being prayed for, the survival rate seems to go down. It is said that this may be due to being told you are, "being prayed for", is the same thing as confirming, you are suffering a fatal condition.

I believe that positive energy helps healing in many ways. So just be positive in your own way.

It could be a placebo effect...

Check out the study posted by Victoria below. You need only read the abstract. A pretty concise study although other possible interventions may skew results like the ability, frame of mind of key surgery team etc. but it’s a pretty large sample so not likely to effect in any substantial way.