Dear Adroser,
It is difficult to say exactly what is going on here. Sometimes, a chest x-ray can demonstrate an enlarged heart due to poor radiographic technique; if the film doesn’t show a deep enough inspiration, the heart can look enlarged and it can make it look as if there is extra fluid in the lungs. However, if this is not the case and there is actually evidence of an enlarged heart, the most likely cause for this could be what is called myocarditis. This is an infection of the heart in which the heart muscle is infected, typically by a virus. Between the viral infection and the immune response to the virus, the two processes can damage the heart and lead to decreased heart function with congestive heart failure, inability of the heart to meet the body’s needs. The heart does not enlarge just due to “fighting an infection.” A cardiomyopathy is a general term that is used to describe diseased heart in some way. Myocarditis can lead to a dilated cardiomyopathy, although there can be other reasons for dilated cardiomyopathy, such as genetic or anatomic. I agree that a pediatric cardiology evaluation would be helpful in this case, and should determine if there is actual disease in your son’s heart, or not.
I also forgot to mention two other symptons. This evening we noticed he had very obvious looking purple reddish circles under his eyes. We've never noticed this on him before and thought it very strange.
When he was sick with his fever, he had very rapid breathing when sleeping.
The pediatrician also mentioned that he was breathing from his belly instead of his chest and it would invert below his sternum.