According to Wolfram|Alpha, there are various mathematical equations that produce a graph in the shape of a heart. A simple example is the following equation: r(?) = 1 - sin(?), which produces a curve called a cardioid, meaning "heart-shaped."
Another option would be to solve the following sixth order algebraic equation: (x² + y² - 1)³ - x² y³ = 0. This equation represents a cross-section for y = 0 of a three-dimensional shape called the heart surface. Finally, a third heart-shaped curve can be defined as such: x = 16 sin³ t; y = 13 cos t - 5 cos (2 t) - 2 cos (3 t) - cos (4 t).