Yes... is does happen. At an appointment with my father last summer, his cardioligist just happened to do a "social" listen while we were in his office. He reacted within 4 seconds that I had aortic stenosis. I had just played hockey the night before and was feeling great (for a 56 year old) Needless to say, he became MY cardiologist that day and I went for EKG, echo, etc... and had surgery within 3 months. My direct family was OK with it as we were used to this surgery (dad has had 4) but many other people were not sure how this could happen. I was fine, active and virtually symptom free. I have since learned that my sometimes shortness of breath and slight dizziness was not becuase I was getting old and over tired... it was a valve that was closing up. I was famiiliar with the cardiologist and surgeon as they had saved my father multiple times and did not get another opinion... but, if in doubt at all, get a 2nd opinion.
Bottom line, you may never know you have a problem... and then !! --- be thankful you found out !! Good luck and ask questions. any and all questions !!