(x^2+y^2-1)^3 - x^2y^3 = 0
or in METAPOST
% Thanks D.E.K. MFB page 134
heart:=(100u,162u)..(140u,178u){right}..(195u,125u){down}..
(100u,0u){curl0}..{up}(5u,125u)..{right}(60u,178u)..(100u,162u);
(* jcl *)
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