Miley Cyrus Miley Cyrus

Tween queen Miley Cyrus has written songs about her broken heart, but in her new autobiography she writes about an actual heart affliction.

Cyrus has a condition called tachycardia, which causes her heart rate to speed up. "The type of tachycardia I have isn't dangerous," she writes in her new book, Miles to Go. "It won't hurt me, but it does bother me. There is never a time onstage when I'm not thinking about my heart."

The book also addresses her broken heart in a chapter to her "Prince Charming," perhaps one Nick Jonas. "Wow! I was so in love," she writes. "Do you know what I'm talking about? The kind of love where the sun could shine or not shine all day long and you wouldn't care."

After their breakup, that love turned to hate — at least in the form of her song "7 Things I Hate About You."

"I was angry when I wrote '7 Things,'" she writes. "I wanted to punish him, to get back at him for hurting me. It starts with a list of what I 'hate.' But I'm not a hater. My heart knew from the start that it was going to turn into a love song. Why does he get a love song? Because I don't hate him."