Trying to figgure out what was wrong with my cat, postmortem.

[Gaius]

Hello. I apolagise in advance if this is the wrong spot to be asking for help with this, but I'm looking for any answers I can find.

Two days ago I came home to find my cat dead.

He was aBurmese (perhaps Bombay) Panther
-Male
-7 years old
-solid and 26lb (very little fat to him. just a proportionally large cat)
-Completely indoor, never been outside and rarely saw other pets.

I arrived home from work and found asome rather gooey stool on the floor in the basement, with a very small amount of coughed-up blood within a few feet.
I found my cat (Crosbie) a few feet further lying in one of the spots he usually sleeps, with the carpet heavily stained with blood in a pattern that looked as if he were moving a lot in the about 1 square-foot area, and blood (and what seemed to be a very small amount of black liquid) on the floor from his mouth.

My mother had seen him 2 hours prior, behaving and reacting normally with no signs of anything wrong.

I'm really looking for some closure. I scourered the house making sure he did not eat anything that could have hurt him, and of the very few things I am not 100% sure he did not get to would have caused completely different, much less severe symptoms.

We have narrowed it down to a severe heart-attack, and perhaps tainted food.
-We had just gotten a new bag of Purina Indoor Cat Chow -the brand he has had since a kitten- and it had been less than a week since he'd been eating the new bag.

The only concerning symptoms of anything he showed recently was odd breathing about 3 weeks ago, which went away after a day when he was given anti-hairball paste.


Sorry for the wall of text, but any insigt would be greatly appreciated.