Any drug such as that effects the body. Cocaine speeds up the heart rate and I think a heart murmer and cocaine just don't mix.

Ceb is correct here. Cocaine is dangerous enough w/o any pre-existing conditions. If you or anyone you know is using cocaine with a heart murmur, please try to convince them that they are putting themselves in real danger.
Short-term cocaine effects include:
increased blood pressure
constricted blood vessels
dilated pupils
mental alertness
increased energy
increased heart rate
decreased appetite
increased temperature