The increase in weight an abdominal girth is probably not from the medication. The heart tumor your dog's vet diagnose probably precipitating a condition called congestive heart failure (also seen in humans). A dilated/enlarge heart is not a effective heart. This leads to blood pooling in the heart. This cause a blood to pool in the whole cardiovascular system and the water component of the escapes out of the circulatory system. This fluids acumulates in the lungs causing cough fatigue and decrease exersice tolerance. The fluid also escapes to the belly and causes increase abdominal girth. Lasix is a diuretic that attempt to reduce this excess fluid and reduce symptoms. So you see lasix is probably not the cause of the symptoms. Your dog is probably having rapid progression of his medical condition.
Since your vet felt a tumor in addition to the enlarged heart, my guess would be that the tumor is what is putting on the weight. It's apparently growing very large, very fast. Did your vet give you any idea of what kind of tumor he thinks it may be, or give you any idea of how much time you may have left with your dog? I think you need to go back to the vet and get some general guidelines on what to expect as the disease progresses. I'm so sorry for you both. :-(
jojo (schnauzer) was a perfect very active dog with a small cough. his appetite was huge. we took him to the vet for his yearly shots. the vet said that he wasnt going to give him the shots cuz his heart is enlarged and has a tumor. they couldnt put him asleep to do some testing cuz he would die. they gave us lasix now for over 6 weeks. my dog was perfect in all ways and we were shocked and still are of this diagnosis. ever since that day he is progressing worse, and he has gained at least 5 lbs in 6 weeks and his stomach is huge and his cough is horrible. he is drinking more, but has to be coersed to go potty and doesnt go very much. i am wondering about the lasix and why he is gaining so much weight ever since being put on the drug. he wasnt overweight but now can hardly carry his stomach - all happening in 6 weeks after being on lasix. his appetite still is huge.
What is the dosage/kg for a dobie?
basic pharmacology , compute the dosage per kilogram body weight...