So these are three GUITextures? Instead of using tags, I would use a GameObject array and then just disable elements from there. So, something like this:

var hearts : GameObject[];
private var clickCount : int = hearts.length;

function Update () {

if(Input.GetMouseButtonDown(0)){
    var ray : Ray = Camera.main.ViewportPointToRay (Vector3(0.5,0.5,0));   
    var hit : RaycastHit;    
       if(Physics.Raycast (ray, hit, 100)){
         if (hit.collider.tag == "click") {
          hearts[clickCount].enabled = false;
          clickCount--;
         }
       }
    }
}

Simply tag the object you want to click with the 'click' and add your GUITextures to the hearts array and you're good to go. :) I think it should work, but I created on air so I'm not so sure if it will ...

Hope that helps, Klep