I agree with a number of the earlier posters. I would still consider asking your cardiologist about taking a diuretic. Even if you don't show swollen ankles or other obvious symptoms, it doesn't mean that you body isn't hoarding water in unexpected places.
I showed no symptoms of having any excess water in my system. No leg or ankle swelling or noticeable weight gain. I wasn't even asked to wear the special stockings in the hospital after my valve surgery.
However, a year after the surgery, I was having lots of trouble moving after I ate, felt stuffed and inflexible, even after a small amount of food. When trying things to get me off of my beta blocker, my cardiologist tried me on some hydrochlorothyazide, a diuretic. I lost about three pounds over a few days, and felt absolutely wonderful again. It also enabled me to cut my beta blocker dose in half at the time (I've since halved it again for over a month without affecting my BP, and am now trying going without it altogether).
Best wishes,