drawing a heart shape with PHP image functions

This PHP code (suggested by the user Licson) draws a star all right:

<?php

header("Content-type: image/png");

function drawStar($img,$x,$y,$radius,$sides,$color,$spikness=0.5) {

    $point =array();

    $t = 0;

    for($a = 0;$a <= 360;$a += 360/($sides*2)) {

        $t++;

            if($t % 2 == 0) {

                $point[] = $x + ($radius * $spikness) * cos(deg2rad($a));

                $point[] = $y + ($radius * $spikness) * sin(deg2rad($a));

            }else{

                $point[] = $x + $radius * cos(deg2rad($a));

                $point[] = $y + $radius * sin(deg2rad($a));

            }

    }

    return imagefilledpolygon($img,$point,$sides*2,$color);

}

$width = 600;

$height = 600;

$image = imagecreate($width, $height) or die("Failed to create stream");

$bgcolor = imagecolorallocate($image, 255, 255, 255);

$curvecolor = imagecolorallocate($image, 211, 211, 211);

drawStar ( $image, 300, 300, 80, 5, $curvecolor, 3);

imagepng($image);

imagedestroy($image);
?>

I would like to draw with the PHP function imageline() a heart shape. I found mathematical formulas for a heart shape, for example: Mathematical equations of love, heart or Heart Curve, and I would like to plot such a function.

However, I cannot figure out how I can translate such a mathematical equation into a functionng PHP code.