My cat died suddenly. Is my other kitten sick, grieving, or poisoned?
I am so very sorry for your loss. I can't image how surprising and upset that must have been for you.
The best way to find out why you're little boy passed away would be an autopsy. Without an autopsy, my best guess would be heart disease. Cats get a heart disease called hypertrophic cardiomyopathy, where the heart muscle is abnormally thick and doesn't pump blood effectively. Often and tragically the first symptom of this disease is sudden death.
Little One could be grieving the loss of her brother - this is quite common. The surviving pet's routines and life are suddenly different and their playmate is gone, so they experience true loss.
Depending on how recently your boy passed away, I might be concerned about a toxin making them both sick. If you know about any potential toxin exposure or if there is mouse bait in or around your home, Little One needs to go to the emergency vet right away. I would be most concerned about a toxin if it was within the last 12-24 hours that your boy passed away. Beyond that, it's unlikely that it's effecting her so much slowly.
All in all, if she's really acting strange, not eating, sleeping too much, having any vomiting or diarrhea, it would be best to take her to the emergency clinic for an exam. If you still have your little boy's body, doing the autopsy could ease your mind as well.
Please accept my condolences during this difficult time.
Updated on September 23rd, 2025