What type of Heart Problem is this?

My friend has a heart problem; his body basically can't create it's own energy so his doctor told him he has to drink lots of water and eat lots of food. If he doesn't he could possibly die or end up hospitalized. He tends to drink monster energy drinks as well for energy. And whenever he's not home right away after school his mom gets worried about him. I want to know what he has is called.
What type of Heart Problem is this?
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