This is a piece of heart as seen in the 3D Zelda titles (save for Twilight Princess). Collect four of these (or five in Twilight Princess) to get another heart container. these are littered through out the overworlds, caves, and various mini games in the Zelda series. There were never found in dungeons until Twilight Princess.
Modeled by Anthus/ AlexRex. EDIT: For some reason, the red heart inside does not show up in the 3D view. Download it, and it's there though.