Looking for an old bear attack movie

I have a very traumatic memory of such movie that I watched as a kid on TV, around 1980, when I was 5-6 years old.

I'm not sure why but I have been searching everywhere for this movie, looking through pictures and summaries of bear attack movies from the 60's and 70's, but so far I didn't see anything that resembles the few fragments that persist in my memory.

A violent bear attack happens. I'm not sure what kind of bear that was, or even maybe some mutant or fictional animal, but it was bear-like for sure. All I really remember is the victim just after the attack, a man covered in blood and gore with his neck and chest torn to shreds. He is there sitting in the ground, with his back laid on a tree. You think he's dead, but - that's a very murky and confusing memory, mind you - after a few moments, while the camera pans through his wounds, you can see his partially exposed heart starting to beat again, or, maybe, some kind of convulsion. But a slow but loud heartbeat sound is featured.

That's likely to be the first violent scene of that movie, because at this point my parents realized that it wasn't a good idea to let me watch the rest of it. I was so frightened that I could barely watch through my fingers. Therefore I can't really tell anything more about it.

I was traumatized for months and that scene keep playing in my head whenever I was trying to fall asleep at night.

Curiously this repressed memory rushed back to my mind while watching The Revenant!