please hold on...I just lost about 10 minutes worth of typing to you.
be right back.
Alright back in action.
We need to clarify a few things said by your vet. I'll have to make some assumptions here.
#1 The heart really will not get smaller, and certainly, not with the medications you are giving. Cardiomegaly or heart enlargement occurs as a compensation for the heart not working correctly. This is generally either due to a condition that dilates the heart so it doesn't contract as good or due to problems with the heart valves. That will not reverse.
#2 The fluid in the lungs. If by now, your vet has not mentioned the term "congestive heart failure" you need a new vet.
This is what happens when the heart is not pushing the blood forward like it should. You get congestion in the lungs. Now, the medications you are using are designed to help that. Specifically, the furosemide, which is a diuretic and pulls fluid out of the lungs.
#3 Now, the ongoing cough. We need to distinguish between fluid still remaining in the lungs (essentially, the medication being given is not good enough), the heart not contracting good enough, and often, a enlarged heart will push on the lungs causing some general coughing.
Well, the enlarged heart pushing on the lungs: that cough can be controlled with simple cough suppressants. Happens a lot. But!!!!! You must be certain that there is not fluid remaining in the lungs before you start it. Otherwise, you cover up the problem allowing fluid buildup in the lungs to get worse.
A good vet will be careful about this and ensure to recommend recheck x-rays to know how the lungs appear.
Also, there are other medications like pimobendan (vetmedin) that can actually help the heart to contract. When furosemide (lasix) and enalapril are not enough, this medication is commonly added.
Also, if you really want to do as much as possible, your vet should have suggested or offered to send you to a specialist to do a heart ultrasound. That will tell you a great deal about the heart function and which medications to give.
That's it. So, it sounds like there are some missing pieces to the puzzle. Definitely, it is worth getting a second opinion.