For most cats, the answer is no!
As a general statement, cats that are on correct types and doses of heart medications will have no fluid on their lungs and therefore will feel happy and act normally.
Unfortunately for a minority of cats, a stroke or blood clot may occur as a part of their disease. This most commonly travels to their hindlimbs and is painful for the first 24-48 hours. This is more likely to occur in cats with heart disease that have not yet been diagnosed and are therefore not on blood thinners to reduce the risk of a clot forming
For some of our feline patients there will come a time when the medications are no longer able to keep the lungs clear of fluid. This is a difficult time for owners and vets. If this time comes, we hope that with good communication and accurate information, owners will feel reassured that they have done all that they can for their cat and will feel as though they can make a decision they are at peace with if euthanasia needs to be considered.