Lasix (furosemide) is a loop diuretic and it inhibits the uptake of sodium (salt). And where ever salt goes, the water goes w/ it. Lasix can cause electrolyte imbalances, but as long as the diet is healthy along with water replacement, your dog should be ok. The accidents are not the dogs fault. But consider the alternative. Being unable to breathe is just straight up suffering. Be sure to follow up with the vet constantly. Walk your dog twice as much as you used to. If the water continues to build up in the lungs, pneumonia can easily set in. An anti-biotic may be required with Lasix therapy. I understand what's happening. Our 13 y/o mini-pincher eventually died of CHF. But in the end, he did well for a time because we got him treatment so his last days were good days and he could breathe. G'luck there!
Been there, done that.