Prayers don't help heart surgery patients.

An excerpt from research on intercessory prayer by Harvard's Herbert Benson:

In a clear setback for those who believe in the power of prayer, their prayers were not answered. Prayers offered by strangers did not reduce the medical complications of major heart surgery. Not only that, but patients who knew that others were praying for them fared worse than those who did not receive such spiritual support, or who did but were not aware of receiving it.

Prayer is an illusion -- a video comparing the impact of praying to God versus praying to a jug of milk.