Really random question about heart disease?

I'm trying to write this story about a teenage boy who has a problem with his heart. What are some heart diseases that could fit this description. I guess it doesn't really have to be a heart disease, any disease, really. It has to be something that he can usually function on a daily basis, but then he has a serious relapse (or whatever the term is) and is hospitalized, in need of a heart(/or another surgery depending on whatever suggestions you guys give me) transplant. I know this question sounds a bit dumb, but I don't really know that much about this kind of issue...thanks

Teenage boy so congenital heart defect would fit.

Let's go with mitral valve prolapse. He then get a bacterial infection seeding into the blood stream (sepsis). Next, he develops infective endocarditis (bacteria growing on the valve). It causes scaring and further damage the defective valve. Then he needs surgery to replace the valve with a prosthetic one.

Good luck

He could have a viral cardiomyopathy. That is a virus like a cold or flu, but it infects the heart, and suddenly the heart gets very, very weak and a young person could urgently need a transplant. You would have to check details online if you use it in a story though to avoid having wrong details in your book.
The other is Wolff-Parkinson-White syndrome, which causes blackout like fainting spells. He would need the electrical system of his heart treated with "ablation" in the hospital. Also called WPW.

he could have a hole in is heart and if u get it publishd and it becomes famise u should say too
mandie hick who is loveing and crap like that lol jkng