Decipher the greeting card $( X^2 +Y^2 -1 ) ^3 - X^2 Y^3 = 0$
Using Maple it is:
[> with(plots):
implicitplot((x^2+y^2-1)^3-x^2*y^3 = 0, x = -10 .. 10, y = -10 .. 10);
http://mathworld.wolfram.com/HeartCurve.html
Have a look at the second graph here
It is a cardiod curve.
Your friend had a great equation for his greetings, check the graph below