car·di·oid 
(kärdē-oid′)
(kärdē-oid′)n.
A heart-shaped plane curve, the locus of a fixed point on a circle that rolls on the circumference of another circle with the same radius.
cardioidThe parametric equations of this cardioid are
x = -a cos θ (1 - cos θ),
y = a sin θ (1 - cos θ).