Tom, an enlarged atrium is fairly common, even for us young guys. Usually it is from a mitral valve not seating fully and causing regurge or a slight backup of blood. If listened well with a stethoscope, you can hear a slight whisper when that part pumps. You could live a normal life with this and never have a problem. It also can come from hypertension-high blood pressure, as the left atrium pumps the oxygenated blood into the left ventrical to go into the body, if the pressure is high it can cause a back up making the atrium enlarge. It can come from CHF, Congestive heart failure, I am sure you dont have that, that is usually for older smokers. If the left ventrical is enlarged, with the left atrium it usually means CHF. There are obvious signs of CHF besides that. I think they just want to make sure there is no underlying problem, and it is most likely the mitral valve problem. Nothing to get worked up over.