Aww I'm pleased to hear she's back home and doing well on her diuretics - I bet she's loving all the fuss now she's back
The main thing with heart disease and heart failure is not to assume that all hope is lost or think that she's dying so you should just keep her comfortable. This absolutely isn't the case. She may be an older lady but if she's otherwise fairly well in herself then it's certainly worth treating her heart disease

Many older cats who suffer with advanced heart disease will die of something completely unrelated before the heart disease becomes fatal if it's treated correctly.
This is just my advice based on what I know.. don't take it all as fact but hopefully it might help you think about your options. I apologise in advance for going into "fact mode" but there's not an easy way to sugarcoat all the information so I've just sort of laid it all out in the hope it helps you to understand Millie's condition better. Please give her some fusses from me
So, the diuretics Millie is taking will dry out the fluid as it builds up in her chest but they won't prevent the fluid from building up in the first place. The congestive heart failure is just a symptom of her underlying heart disease and by treating her symptoms but not addressing the cause you may struggle to keep her out of trouble. If the vet is fairly certain of the diagnosis of heart disease then she ideally needs an additional drug to control her blood pressure and help her heart pump better and she also needs to be taking a blood thinner called Plavix, or alternatively baby aspirin to prevent blood clots.
Whether or not you decide to go down the route of having further tests done, I'd certainly discuss adding these drugs to Millie's treatment if the vet hasn't discussed them already, as the diuretics alone won't keep her heart condition under control and you may find she relapses suddenly or gets a blood clot. Clots unfortunately can't be prevented but the risks can be minimised by treating with a daily blood thinner and it's vital that if she has advanced heart disease that she takes something to lower this risk as blood clots are just awful and usually fatal.
Also, under no circumstances should Millie be taken off the diuretics. The vet may decide to lower the dose after an initial fluid buildup is under control but she shouldn't ever be taken off them. Some vets who aren't overly familiar with heart conditions will suggest that diuretics are removed once the fluid has been successfully treated but unfortunately this just allows for the fluid to build back up again. The diuretics will be required for the rest of her life in order to keep the fluid under control. My vet didn't have a great deal of experience with heart conditions and she suggested taking the diuretics away after 3 weeks but thankfully I spoke to a cardiologist before I did and he said that I absolutely mustn't take the diuretics away. If your vet has experience with heart conditions then they should be aware of everything I've mentioned above but many vets aren't specialists in heart disease as they're more like GP's and obviously can't understand every single illness in great depth. That's not to say they're not good vets, they just can't know everything. Certainly it's important to trust your vet but do ask questions - they'll look into anything you ask if they don't know the answer, my vet did
The heart scan the vet has mentioned may be an echocardiogram and this can be done while she's awake if she'll tolerate it but it will require her to have a patch shaved from her chest. The echocardiogram takes an indepth look at the heart and will show how the heart is pumping and will allow the vet to measure the thickness of the heart walls and confirm what stage Millie's heart disease is at. Alternatively, if your vet doesn't have the equipment for an echo (as these are often done by a cardiologist) then they may be looking to do an ultrasound as this is less detailed but will also show up any abnormalities of the heart.
The blood pressure test is similar to that a human would have so neither test is particularly invasive and both the scans and BP tests can be done without sedation or anaesthesia in many cases, but they do require her to go into the vets for a few hours and if she won't tolerate the tests then they'd have to sedate her. Given her age and her condition, sedation is fairly risky so I'm not sure I'd want that if she were mine.
It was risky enough for Harvey (he had to be sedated as he's not at all tolerant of being poked) when he was poorly but he's only 5 and didn't have any other health issues.
They can also use a simple x-ray to look for enlargement of the heart without doing the more advanced echocardiogram test (again, if she sits still they can do this while she's awake) but the x-rays give limited information. However, an x-ray is far more straight forward than an echocardiogram or ultrasound and could be enough to show up enlargement which would confirm the heart disease diagnosis and at this point, confirmation of that is all you really need to be sure you're treating her for the right condition.
If she's fairly laid back then it may not phase her too much and the tests will give the vet some figures to work with regarding how advanced her heart disease but given that she's already in congestive heart failure I'd expect the scans will only confirm what you already know.
In a younger cat the vet would do all the scans and then create a treatment plan to help the cat live a healthy life for as long as possible, as with the right care they can sometimes go for a couple of years after congestive heart failure occurs, but given Millie's age it may not be worth putting her through the stress involved just to confirm the diagnosis. The vet can treat her for heart disease without the test results, it's just not an ideal scenario as obviously they're not certain of what they're treating.
I think if it were me I'd perhaps just discuss treatment options with your vet and see if they'd be happy to treat for the heart disease on the assumption that it's fairly advanced.
You could look at the BP test as that's a lot less stressful than the other tests and will at least give the vet a little information to go on, but only you and your husband know whether or not Millie is likely to be stressed by having it. Your vet may not be prepared to put her on any BP medication without at least performing this test as it if it turns out her BP isn't high then it could be dangerous.
The general drug treatment for heart disease and CHF is a combination of three drugs and is fairly standard:
- Benazepril, Atenolol or Semintra - These are all designed to lower BP and help the heart pump better. As I mentioned in my email, Semintra is usually used for kidney disease so it could be a good option and it's a liquid
- Furosemide - A diuretic to keep fluid off the lungs - I believe there's a liquid version of this available if required - ask your vet if you think you need it
- Plavix or baby Aspirin - This is given daily in advanced heart disease patients to prevent blood clots as a cat with advanced heart disease can throw a clot at any time and these are usually severe and often fatal
I hope all of that helps, I'm sorry for all the overly factual info there but hopefully it gives you a better understanding of what you're dealing with. If there's anything there that doesn't make sense then feel free to ask as I know that was a bit of an information overload
Good luck with everything, whatever route you take. It sounds like Millie is at least feeling much better right now and hopefully that continues for a good while to come; I'm sure it will with all the love and fuss she'll be getting
Take care
Sarah