What predators does the eastern diamondback rattlesnake have?

Rattlesnakes, a kind of viper, have a very complex venom. Mostly, rattlesnake venom is a somatic toxin, which means it's not very neurotoxic, but instead attacks a lot of systems in the body.

The toxin contains enzymes that denature proteins and destroy collagen (a connective tissue) in a process that has similarity to digestion. Also, a large part of the toxin includes cellular destroyers which cause apoptosis (cellular self-destruction) and lysis (blood cell destruction). There is some neurotoxic effect in that it also contains acetylcholinesterase (ACE) that act to "turn off" straited muscles (like your arm or leg) and prevent turning on smooth muscles (like your blood vessels and heart).

There are many components and processes in viper herpetoxin that we don't understand yet.

As bad as all this sounds, very few rattlesnake bites result in a fatality, although tissue destruction (necrosis) is not uncommon in bites where toxin is delivered. About 20% of all Rattlesnake bites in America are "dry bites" in which no toxin is delivered.

It appears that the determinant factor that limits the amount of damage done in envenomating bites is the amount of time between the envenomation and medical (not first aid) treatment.