First, just to note, that even with heart issues or gum disease, we should still be seeing pink gums. Or at the very least, you shouldn't be seeing any changes from Lucas's normal. In any case, this vomiting and belly discomfort isn't likely related to those known health issues and instead we'd be concerned about a bacterial or viral GI bug, pancreatitis (especially with the belly pain), dietary indiscretion, or possibly secondary to other organ or metabolic issues.
Now if he is struggling to keep water down, then we need to tread with care. Not being able to do so at all can be a hint that we will need to use injectable anti-vomiting medication at least initially to settle this severe nausea. That said, if he can keep a bit down, then there are some supportive measures we can try at this stage. Specifically, as long as he hasn't just vomited (since otherwise we may need to rest the stomach and just give sips of water for a few hours first) you can start him with an antacid. There are a number of antacids that are available over the counter and pet friendly. I would advise only treating with one, but the ones I tend to recommend are Pepcid (More Info/Dose @http://www.petplace.com/article/drug-library/library/over-the-counter/famotidine-pepcid) or Zantac (More Info/Dose @http://www.petplace.com/article/drug-library/library/over-the-counter/ranitidine-hcl-zantac). We tend to want to use these 20 minutes before offering food to allow it to take effect.
Once that has had time to absorb, you can consider tempting him with a light/easily digestible diet. If you do so, start with a small volume (a spoonful) to start. Examples would be cooked white rice with boiled chicken, boiled white fish, or scrambled eggs(made with water and not milk). There are also veterinary prescription diets that can be used (ie Hill’s I/D or Royal Canin’s sensitivity). When you offer that spoonful, give him 30 minutes to settle. If he keeps the food down, you can give a bit more and so on. As his tummy stabilizes, you can offer more. The aim of the easily digestible diet is that it will be better tolerated and absorbed by the compromised gut. Therefore, it should get more nutrients in and result in less GI upset.
Just to note, since dehydration is a real risk here, we need to keep an eye on his hydration. To check this and ensure he isn't becoming dehydrated there are afew things we can test. One is whether the eyes appear sunken, if the gums are tacky instead of wet/moist, and whether he has a "skin tent" when you lift the skin. To see how to check these parameters for dehydration, you can find a wee video on this HERE (http://www.ehow.com/video_12232503_dog-dehydrated.html). If you are seeing any signs of dehydration already, then you do want to have him seen by the vet before this becomes an additional issue for him. (since it is often the dehydration that starts to tap their energy level, depresses them, and makes them feel ill). And this is especially important since we cannot syringe fluids into vomiting dogs.
Overall, those would be our above concerns for Lucas's signs. If he is very sore and struggling to keep water down, then we do need to tread with care and think about having him seen by his vet. Especially if he is very painful, since we don't want that to be lingering for him. Of course, if there is any delay in having him seen by his vet, then do use the above to try to reduce those signs. If he settles, we are happy. But if he remains sore, then we would want a check +/- bloods to pinpoint which issue is present and to get him on injectable pain relief, anti-nausea medication +/- antibiotics to settle this for him.
I hope this information is helpful.
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All the best,
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