Here are some hearts for Valentine's day designed to be easy and quick to print. They were constructed from the number 6 plane curve at mathworld.

http://mathworld.wolfram.com/HeartCurve.html

Five objects are available -

pin.stl - a heart with a fitting for a safety pin
box.stl - a small box
lid.stl - a lid for the box
pendant_mark_01.stl - a single sided pendant
pendant_mark_02.stl - a double sided pendant

OpenSCAD code is included.

The lid and pendant_mark_02.stl need to be printed with support. The pin can be printed directly on the build surface but has a more finished back if support is used.

Pendant_mark_01 and the box can be printed directly on the build platform.

A safety pin can be installed on the pin's back and secured with a small piece of 1.8 mm printing plastic.

Glueing two single sided pendants together makes a nicely finished version of the double sided pendant.