Reminder: please read the "Notes" at the cat Facebook page and the blog's Medication tab and other tabs for what your cat should be taking and why.
A HCM cat often needs more than just a diuretic. There are drugs to boost the heart or slow it down, and to protect the heart's ability to properly function. And vitamins and supplements are also key, for the heart/body function/kidneys, especially as the need for a diuretic increases. I strongly urge you to administer them to your cats. Your cat's body needs to replenish what the diuretic takes out-electrolytes, especially potassium. The cat needs to be hydrated as diuretics dehydrates-feed mostly wet food not dry; add water to food and water by mouth as needed but especially when pilling.
Keep up the med schedule as prescribed. Don't delay!! This is crucial. Keep a notebook-write down reactions to situations, meds, does the cat seem dazed/slow/unsteady in its gait, etc.-every little blip you see and discuss it with the vet. Could mean a reaction to med, meds need adjusting, could be a new situation occurring in the heart, could be electrolytes are too high/too low, etc.
Know your electrolytes, how they function, how they are interrelated to the body's function: potassium, sodium, chloride, glucose, magnesium, bicarb, phosphorous, calcium. Understand how if they are too high (hyper) or too low (hypo) they can cause issues. You will need to replenish potassium for sure, and give magnesium and bicarb as needed for kidney support, and glucose-as long as the cat's not diabetic-for when it needs energy support in times when it's not eating well enough (a drop of corn syrup or condensed milk in 1/4 cup of water for example.)
A simple CBC/chem panel blood test will show you a range of results for electrolytes and other blood chemistry items being tested.
The different tabs at the blog have links to websites that explain all of these. I recommend reading Wikipedia, Drugs.com, MedlinePlus website, etc. Find a website that is easy to read, that doesn't get you caught up in ads or scrolling through photos of information-which are a waste of time. The more you know, the better your cat will be as you will be able to do more for your cat. Good luck!