Has anyone had to do this if a horse is over excited and you can not clam them down? Are there certain traq's to avoid if they would harm the horse in any way?

I haven't yet had to sedate a horse, but I can tell you to never use morphine. Morphine is used to sedate and relieve pain in many species including humans, but in horses and cats it causes a great deal of hyperactivity and excitement, and the horse is very likely to hurt intself.

Since dogs are domesticated like cats, would that be the same for them? I have seen some dogs that well past the puppy stage are hyper and if thats the case, couldn't they die from a heart attack or something similar?

Some humans are hyper well past childhood as well. I don't think tranquilizing something because its hyper is necessarily a good coping tool. Your first tool for a horse would be a twitch in most cases for an immediate fix. Long term the animal would need trained to have less anxiety in situations through repeated exposure.

tiki thats what I was wondering too. I think some end up using the tranq as a quick fix, but it never really solves the underlying issue for long term.