<human>: It was actually yesterday, but I went over to my cousin's house who recently had heart surgery to cheer him up. He's relatively young, but has a congenital defect of his aortic valve.

I go visit him to cheer him up, since he's pretty limited regarding his level of physical exertion. He has (had) a cat. A fat one, who is supposed to be on a diet and getting more exercise, so we were entertaining ourselves by letting him chase a laser pointer around the room and up the wall, etc. 

After a few minutes, the cat slowed down considerably, so we decided we were going to give him a rest, but just as we stopped, he toppled over on his side and stopped moving. No panting, no breathing no nothing. I get up and run over to him and his eyes are wide open and he's lifeless. 

I tell my cousin, and decide I'm going to try CPR on the cat. It turns out that I'm not very good at animal CPR, even though I'm training in human CPR. It didn't work, so we took the recently departed cat to the animal clinic to find out that we probably gave him a heart attack. 

I've felt so fucking horrible, my cousin is recovering from major heart surgery and this isn't exactly the stress he needs.

Provide a brief overview of the text.
<bot>: My cousin had heart surgery, so I tried to cheer him up by accidentally giving his cat a heart attack and giving him a permanent cat nap.