After my mom passed away suddenly, I had to take her elderly cat home with me on a one hour flight. I loved the cat and I was terrified that it would be too much stress for her. It was incredibly stressful for the cat, she peed and pooped in the car on the way to the airport, but the calming caller I bought her (A desperate last stop just before the airport) really seemed to help. That’s not really related to what you’re talking about, but it’s validating to hear that cats that are extremely stressed out could indeed have heart attacks.