- a somewhat heart-shaped curve, being the path of a point on a circle that rolls externally, without slipping, on another equal circle. Equation: r = a(1−cosA).
- a heart-shaped curve generated by a fixed point on a circle as it rolls around another fixed circle of equal radius, a. Equation: r = a (1 – cos φ), where r is the radius vector and φ is the polar angle
