Heat vs Ice?
There are two basic types of injuries, Acute and Chronic.
An acute injury is typically caused by something, a collision, fall, sprain or some sort of trauma. There is usually significant pain, swelling, maybe bruising, and this is what you want to limit. So for an Acute injury you want to use ice.
A chronic injury is usually non-traumatic, subtle and slow developing. Typically this type of injury is not associated with swelling so it is safe to use heat with chronic injuries.
The rule is, if there is swelling use Ice.