Pete, thanks for stressing that, it's a  very good point.  The only time I have seen heat used is with VERY localised stings from bees etc.  and it was very localised heat.  If the venom has become systemic, icreasing the circulation could be a really bad thing.  It would also make it harder to treat with HVDC, where a localised reaction is a must.  I must agree with you  DO NOT USE HEAT ON A SNAKE BITE  <img src="/images/graemlins/shocked.gif" alt="" />
Macgyver.