i am so sorry that you went on web md for advice about your dog. hopefully you took your dog to the vet in time. yes dogs can get congestive heart failure. weight gain is a sign more in the chest area as you had said your dog was gaining. there is no reason a dog would gain like that on the same amount of food or cutting back on the food except if you went from given exercise to zero exercise. the only other reason is medical. the weight gain is from fluid retention most likely. they could also be suffering from another issue. that is how it happened in my dog she looked very heavy in the chest. the most common cause for it is advanced cancer. with my dog she lost weight even still her chest looked larger. the tumor was in her throat and she had trouble keeping food down. unfortunately just like in people the most you can do is make them comfortable drugs that help expel the fluids and as long as your dog is happy and pain free love them as much as you can until it is time to put them down. you should never let your dog suffer and trust me you will know when it is time. i truly am sorry you were given such a extremely uneducated answer but it is web md and not vet md. they possibly thought that it was the correct answer not sure how possibly they never owned a dog before.
can my dog have cogestive heart failure? . my 2 1/2 year old female sheltie will not let me "rub her tummy". while doing her tricks she can't roll over. she has gained weight over the winter but almost 2 pounds in the last week. her chest is larger than normal which could be the cause of weight gain. we limited treats. went from active dog food to light. we have limited the amount to 1 1/2 cups of dry dog food she continues to poop but seems to be more constipated.