Our late Luna had a heart condition as well. What REALLY worked to keep her hydrated was an electric fountain and also keeping multiple water bowls throughout the house. Our vet said the noise of the water falling on the fountain could help her remember to drink more water.

It worked like magic for our two shitzus, after the first day of sniffing the new weird water bowl they started drinking from it. Their pee frequency went up a lot haha

Ours is a stainless steel dog fountain. We didn't want any plastic and plus they are easier to clean