Instagram Shots: Justin Bieber Goes Shirtless

If there was ever a photo that cause heart attacks in teenage girls, it was probably this one. Justin Bieber posted this shirtless photo on Instagram without a caption ... likely because he knew darn well that he didn't need one.

A picture speaks a thousand words, anyway -- though most of the Beliebers who saw this one probably couldn't muster any beyond gasps, screams and squeals.