Hearts Joined

Heart shape via the function:

f(t) =
[18 * pow(sin(t),3),
15 * cos(t) - 5 * cos(2*t) - 2 * cos(3*t) - cos(4*t)
];

You can experiment with function parameters and generate OpenSCAD code on the interactive page

http://kitwallace.co.uk/3d/knot-braid.xq?preset=9

Two joined hearts use a hulled-sphere construction because the standard polyhedral construction doesn't play well with CSG operations in OpenSCAD