Enlarged hard is actaully not the hart in size itself, often. It's the walls inside the heart that gets to big and the chambers gets to small for all the blood that goes true it. The heart is a muscle and it will grow, yes. How much probably depends in doses of steroids and probably a few other things, like cardio. I don't think there is any way of preventing it. Just don't go crazy on the dose and "over do it". Maybe the hart is like every other muscle, in a way. Everyone have one or two places they put on mass very easy. For some it might be easier to get an enlarged heart that for others.