Thank you Suzanne,
If the blood results are not yet back, then hopefully they will hold the answer to Rocky's signs. I would also note that if your vet is truly concerned about endocarditis (bacterial infection of the heart valves), you may wish to speak to them about a heart scan. This would be a fairly non-invasive tool that would allow your vet and yourself to see Rocky's heart and appreciate if there are bacterial lesions on the valves as they suspect. At the same time the vet can check an ECG to appreciate if Rocky's fast heart rate also has an irregular rhythmn that could be caused by this condition. And if this is confirmed, then it would shed light on his situation and give a better idea of his prognosis.
Further to this, without his blood work back nor a heart scan done, we cannot be totally sure that a heart valve infection (which is not very common) is the only thing to blame. The reason is because while kitties with fevers may go off their food, cats that are generally unwell, have sore mouths (less likely here if they have examined his mouth and given a pain killer) or nauseous can do so too. Therefore, it may be worth having your vet cover bases and treat Rocky for nausea to ensure this isn't what is putting him off his food. There are a range of anti-nausea treatments that could be considered and some are even available over the counter. These include Cimetidine/Tagamet (LINK), Famotidine/Pepcid (LINK), Omeprazole/Prilosec (More Info/Dose), or Ranitidine/Zantac (LINK). These may be ones to consider trying for him but I would note that if he is currently getting injections from his vet, it is better to coordinate with them since you don't want to give anything yourself that may counteract something they have given. As well, the vet will also have strong injectable anti-vomiting medications like Metoclopramide (LINK) Ondansetron (More Info/Dose) or Cerenia. So, I would consider first making sure that if he is suffering with underlying nausea that we are addressing it and ruling it out so that you can make sure there isn't something else putting him off his food.
Alternatively, since Rocky is off his food, you may also want to speak to his vet about vet about a trial on an appetite stimulant drug. The two we use most often in cats are Mertazipine/mirtazapine (LINK) and cyproheptadine (LINK). And one of these could just get him back on track to eating while you work together to determine what has put him off his food.
Further to these treatments, that can help get him eating, we need to continue to tempt him to eat (as I know you are). Favourite foods are allowed or you can tempt him with a light/easily digestible diet. Examples of this would be boiled chicken, boiled white fish, scrambled eggs (made with water and not milk), meat baby food (do avoid the ones with garlic powder in the ingredients) or there are also veterinary prescription diets that can be used here (ie Hill’s I/D or Royal Canin’s sensitivity.) This all said, if tempting doesn’t work (which sounds quite likely with Rocky at the moment), then we do have to consider initiating syringe feeds to get food in. In that case, you may want to try Hill's A/D (LINK) or Royal Canin Recovery (LINK) from your local vet. Both are critical care diets that come as a soft, palatable pate. It is calorically dense, so a little goes a long way nutrition-wise and this could just help get some more calories into him even if we can’t get a huge volume of food in. Just to note, these diets are amenable to having water added to make into a gruel to syringe feed if necessary. As well, for syringing food, you can use the animal version of Ensure (balanced for animals dietary requirements) called Clinicare Canine/Feline Liquid Diet (LINK). It is actually by the same people who make Ensure, but is formulated to meet out pet's dietary needs. Your vet should be able to order it for you but it is available without a prescription (some pet stores and even Amazon stock it). This way it would a means of getting food, stopping his self imposed starvation, and this is something you can do at home to get some nutrition into him.
Overall, without those bloods or an official definitive diagnosis, you will be limited on how to approach Rocky's situation at home. That said, you can consider an antacid just now (though do ring to make sure what you choose to give is compatible with what they have given) or have his vet give an anti-vomiting medication to ensure nausea is not playing a role in his anorexia. Further to this, you can speak to them about an appetite stimulating drug to break his fast. But in the meantime, while you are waiting for those blood results, the key here will be to tempt him to eat or (if he refuses) start syringe feeding to break his fast and prevent him from wasting away while you await his vet's findings on the bloods.
I hope this information is helpful.
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All the best,
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