Non-Modular Hearts: 21

Origami designers featured here include Jannie Van Schuylenburg, Jeremy Shafer, and Leyla Torres. Shafer's heart box (see left) requires a single sheet of either letter-size paper or A-4 paper. Torres' heart box (see right) requires a single square sheet, as does Van Schuylenburg's double-hearted party plate (see below.)
 
The reverse side of the paper shows prominently in all of these models, so double-sided paper is a must.