http://1000.chromeexperiments.com/#/editor

heart.js

var spacing = 15;
var size = 10;

var center = new THREE.Vector3( 1, 1, 1 );
center.multiplyScalar( Math.floor( size / 2 ) );

return {
    init: function( particle, i ) {
        var x = particle.index;
        var y = 0;
        var z = 0;

        particle.position.set( x, y, z );
        particle.position.sub( center );
        particle.position.multiplyScalar( spacing );

        particle.originalPosition = new THREE.Vector3().copy( particle.position );
    },

    update: function( particle, currentTime ) {
        var offset = particle.index - 500;
        particle.position.copy( particle.originalPosition );
        if (particle.index % 2 == 1) {
            particle.position.x = offset / 250.0 * 25
            particle.position.y = Math.sqrt(1-Math.pow(Math.abs(offset / 250.0) -1, 2)) * 25 + 25 + Math.sin(currentTime) * 5
        } else {
            particle.position.x = offset / 250.0 * 25
            particle.position.y = (Math.acos(1-Math.abs(offset / 250.0))-Math.PI) * 25 + 25 + Math.sin(currentTime) * 5
        }
    }
}