I was diagnosed by ct scan with mild cardiomegaly. however, every chest x ray shows neggative cardiomegaly. when i look at the photo my heart is visibly enlarged? how are they missing the enlargment? i've had at least 6 x rays all neggative?

Cardiomegaly means, "enlarged heart". It could mean the image on X-rays, a CT scan, MRI; or it could be the image on an echocardiogram. And it might refer to the external measurement of the heart, or the thickness of the heart's walls which, if abnormally thick, contribute to an increase in the heart's mass. Finally, "cardiomegaly" by EKG criteria cannot distinguish which type of enlargement.