A chest X-ray which is read as having a borderline heart size is one in which the size of the heart is at the very upper limit of normal. This means that the actual heart size may be normal or slightly increased. If there is a suspicion of increased size based on symptoms, physical exam or EKG, as well as the chest x-ray, an echocardiogram may be performed to determine if it truly is enlarged. Only your physician can decide if this is warranted in your particular case. If there truly were an increase in the size of the heart this could be due to an increase in the