Music sensation Lady Gaga was forced to pull out of a concert in Indiana on Thursday night after she found herself struggling to breathe.
Just minutes before she was due to make her stage entrance, paramedics discovered her heart was beating irregularly.
The 23-year-old later used Twitter to apologise to any disappointed fans.
"I've been crying for hours, I feel like I let my fans down 2nite. An hour before the show, I was feeling dizzy and having trouble breathing," she posted.
"Paramedics came to take care of me, and told me my heart-rate was irregular - a result of exhaustion and dehydration. I can't apologise enough for how sorry I am. I could hear my fans cheering from my dressing room, I begged everyone to let me go onstage.
"My stage has complicated mechanical elements, everyone was concerned I'd be in danger during the 2hr show, since I had passed out earlier. I am so devastated. I have performed with the flu, a cold, strep throat: I would never cancel a show just based on discomfort.
"I hope you can forgive me. I love my little monsters more than anything, you are everything to me."