A few questions about the heart

[LevesqueIsKing]

I guess I just don't really understand why it's considered a muscle. Why is it the only muscle that has to be worked with cardiovascular exercise? I swear if there was a powerlifting movement that worked the heart I'd have that thing pumping like crazy...but I don't. And since it's a muscle, does that mean that mesomorphs (or people with naturally stronger muscles) have more efficient hearts? That they're less prone to heart attacks and whatnot?

Also, on a side-note, I've had VERY little stamina lately. It seems as though after every single set I do I get light-headed and have to take an unusually longer rest. Does this have something to do with my lack of doing ANYTHING cardiovascular for the past year or two, or some other cause?

[rbtrout]

As far as the heart being a muscle, I'd assume because of how it's made. I've actually been diagnosed with "athletic heart syndrome" or an enlarged heart muscle, which makes getting lift insurance extremely costly or non-existant (unless I go cheap). My cardiologist said it was because I lift quite hard and heavy.
For the stamina issue, I get that way frequently. For me, it's sinuses. A round with some sinus medicine, a back adjustment from my friend (a chiro) and I'm good for quite a while.