Hi there, well done for agreeing to foster a rescue dog! The signs he is showing can indicate a respiratory tract infection (such as kennel cough) but we do also see these signs in dogs with heart disease. Given his age and history, a respiratory infection is more likely. I would ask you to check a couple of things- firstly, his respiratory effort when he is resting, ie is he breathing normally or do you notice his abdomen moving in and out as if it is difficult for him to breathe. The second thing is if you could please lift his lip and look at his gum colour. The pigmented areas will be black but there should be a few un-pigmented areas which should be pink in a dog that is breathing ok. If he is breathing ok and his gums are nice and pink, you should be able to take him to the vet tomorrow as planned and just keep him rested overnight. Please let me know if you have further concerns and I will try to answer them for you.