Disease Information Sites
International Cat Care has some basic information about the different kinds of heart disease in cats and is a good starting place.
The Special Hearts: Cats with Heart Defects or Disease Facebook group has a lot of good information about heart disease in their Files section. You will need to be admitted to the group to view those files.
Tanya’s Comprehensive Guide to Feline Chronic Kidney Disease has excellent information about heart disease in cats. This page does spend time covering the specifics of heart disease in cats who also have kidney disease, but is still worth reading even if your cat does not also have kidney disease.
Many cats with heart disease are at higher-than-average risk of throwing blood clots. Blood Clots and Saddle Thrombus has more information about that complication.
There are a few different support groups that are all great for heart disease kitties. On Facebook, Special Hearts: Cats with Heart Defects or Disease and Cats with Blood Clots (inc. a saddle thrombus): a community support page are both excellent. Joining both groups would be a good choice. Many cats with heart disease are at higher risk for blood clots so it is a good idea to be part of the blood clot support group ahead of time in case your cat also experiences one.
Cats with Multiple Medical Conditions (kidneys, heart, IBD, liver and more) is a science-based group that provides excellent support.
Tanya’s Feline Chronic Kidney Disease Support Group is on groups.io, an email-based support platform. Many cats with heart disease either have kidney disease or will develop kidney disease, so this group is a good one to be aware of.