- print_r: documentation ( source)
- preg_split: documentation ( source)
<?php
$str = "<h3>hello</h3>this is my test and <h3><span>bye</span></h3>";
$arr = preg_split('/(<h3>.*?<\/h3>)/', $str, -1, PREG_SPLIT_NO_EMPTY | PREG_SPLIT_DELIM_CAPTURE);
print_r($arr);