[joeysteele]

It is not normally dangerous to wake someone sleepwalking,however, it is wiser to just guide them gently back to bed.

Clearly if woken and startled they may lash out and hurt the person waking them or fall and hurt themselves,that is why it's recommended to just guide them back to bed.

Also,where the heart attack comment comes in is naturally if they have a known heart condition, waking them is unwise as the surprise element could increase their heartbeat which in a healthy person would have little effect but to someone with a known heart problem then that could be dangerous.