| An inversion element on some steel roller coasters by Bolliger & Mabillard. Typically seen on their inverted coasters, a heartline flip rotates the train in a very small-diameter corkscrew, producing a rotation around the rider's "heartline" in a style very much like a barrel roll. The heartline flip also shows up as a possible element in Roller Coaster Tycoon.
Source: http://www.faqs.org/faqs/roller-coaster-faq/part2/ | 
