I agree with all of the above. I had known for a number of years that my valve was going to have to be replaced "some day", and was being followed up annually by a cardio, echos etc. I did not think I was symptomatic, put my SOB (shortness of breath) down to age (50-ish), weight (too much), inactivity and years of smoking. Once the valve was replaced, my non-symptoms vanished!
Before any final decision is made, the surgeon will want you to have at least a heartcath done. These are more accurate than echos, and provide the surgeon (and you) with a ton more information.
It is hard news to hear, that someone is going to knock you out, stop your heart beating, cut it up and then put it all back together. But these guys know what they are doing. One thought I clung to was that my regional heart cente did more of these in a week than my local hospital did tonsils and appendectomies in a year.
So, get thyself to a surgeon ASAP. The heart is a muscle nd will compensate for any inefficiencies in its functioning. I am still on beta-blockers and BP meds, almost two years after surgery, because my heart enlarged itself tring to force enough blood through my stenotic aorta to get enough oxygen to the rest of me. Trust us, the sooner you get it fixed, the better!