The kidney problem will certainly contribute to peeing in the house - sometimes your pup won't even know it is happening. Re the heart condition, has your vet indicated level of risk in having pup neutered? You obviously have a choice in this case. Should your pup require life saving surgery, then being put under becomes moot (this happened with us) - so you take the risk. Also since the pup is new to your home he will mark his territory and with existing vision problems and other pets is no doubt nervous. Hope it all works out. Expect you will be given meds and maybe specific food for kidney problems - hopefully you won't need heart meds. Very nice of you to rescue the little pup.