Advice on Cat with Heart Disease

[Baxter2020]

Hello,

My cat Simba is now only 3 years old and he was diagnosed with Hypertrophic Obstructive Cardiomyopathy last May 2019. It was found at a really early stage where there was no symptoms of the disease other than a grade 2 heart murmur. In October he was checked again and we were advised that it was still to early to see how quickly the heart disease was going to progress although there was evidence of valve enlargement but only slightly. Over the past year we think he has become a little more tired but not enormously changed. He has been prescribed medication as a precaution to avoid blood clots. Now Covid-19 has hit we cannot get him checked again to see if it's gotten much worse. We live in the country and he goes out for several days at a time now in the Summer and I'm terrified that he's going to have a heart attack without his medication but he's so miserable being stuck in and we can't overly tell if he's hugely worse at this stage.

I would just like to know if anyone has had a cat with this condition and what were the clear symptoms that their heart disease was much worse? It is really obvious as I know cats are good at hiding their ill health?