I'm 64 in pretty good health. i've had echocardiogram, stress echo, and stress echo with contrast. all came out good. shortly after cxr showed cardiomegaly. dr. said don't worry. why shouldn't i?

Your: Enlarge heart on x-ray is something that happens over time. As far as no shortness of breath or on exertion, make sure blood pressure is under control.

Because: All the tests you quoted in your question are more sensitive for detecting any heart disease associated with a possible enlarged heart as reported on a chest xray. Worry will do you no good. Be happy all the more specific and accurate test you had were normal. Best wishes.

Echocardiogram: Chest xrays often are inaccurate in assessing heart size and overread enlargement. An echocardiogram accurately assesses heart size and i would rely on it rather than the chest x-ray.

No cause for concern: Since the echocardiogram was normal, presumably the thickness of the walls of the heart was normal. Therefore, the heart is not actually enlarged despite what the chest x-ray showed. In addition, a normal echocardiogram means that heart function is normal and this is very important. Having a normal stress echocardiogram is also reassuring and significant coronary artery disease is also unlikely.