Heidi Montag -- Oops, My Boob Fell Out!

9/14/2010 7:00 PM PDT

Heidi Montag -- Oops, My Breasts Fell Out!

Heidi Montag struggled to contain herself in Costa Rica last week -- when the reality star's bikini top happened to collapse under the pressure of a G-cup-sized breast ... right in front of the cameras.

Spencer Pratt's loving wife is known for taking things too far.