What is rattlesnake's poison called?

Snake Venom does not have any specific name. It is just referred to as "Rattle Snake Venom"

The Rattlesnake venom is highly Hemotoxic. The venom travels through the bloodstream, destroying tissue and causing swelling, internal bleeding and intense pain. Some subspecies also contain a neurotoxic component in their venom that may cause paralysis. Rattlesnake bites are rarely fatal to adult humans. If an anti-venom treatment is given within the first 1-2 hours, the probability of recovery is nearly 99%.