Thank you, Candace!
The furosemide did not help. We repeated chest xrays yesterday, and there was no fluid present.
The vet saw some mild interstitial pattern (pattern that partially obscures the margins of the pulmonary blood vessels).
So now we are down to rule out either bronchitis (either bacterial or chronic), asthma or some other lung disease (I entered the notes in Monroe's medical record, but I still can't remember what the other thing was).
Monroe got an antibiotic injection in case it is bacterial bronchitis. He is still coughing today.
If it's not bacterial, he needs steroids (which could speed up his heartfailure). He would also have to discontinue Atopica, and he has already developed a couple of sores.
With asthma, he would have to use a nebulizer, which, I think, he would not tolerate.
Sorry about the lengthy post, but it's all so complicated, and I think that his vet is a bit frustrated, too.
But I want to stay positive, and get the best possible treatment for him!