Cardioid heart curve
Equation: (x² + y² + 2x)² = 4(x² + y²)
The polar form r = 2(1 − cos θ) is the same curve as (x² + y² + 2x)² = 4(x² + y²). The cusp sits at the origin.
It is a roulette: a unit circle rolling around another unit circle, in the same family as the cycloid and nephroid.