gistfile1.php

<?php     
$data = '<div>blabla<h1><a href="http://www.example.com/blabla.php?id=12345" class=l>blub</a></h1><h2><a href="http://www.example.com/asfadfafadf.php?id=12345" class=l>blub</a></h2>sdfafgdghaghagh<h1><a href="http://www.example.com/fdgadfhfh.php?id=123dsfasdf45" class=l>blub</a>asdfasdfasdf</h1>'; 
     
$doc = new DOMDocument();
$doc->loadHTML($data);
$elements = $doc->getElementsByTagName('h1');
$link_targets = array();
foreach ($elements as $element){
  foreach($element->childNodes as $child){
		if(get_class($child) == 'DOMElement' && $child->hasAttribute("href")){
			$link_targets[] = $child->getAttribute("href");
		}
	}
}
     
print_r($link_targets);