$re = '/<div(?!>).*?class="myClass".*?>(.*?)<\/div>/mi';
$str = '<div class="test"></div><div></div><div id="foo" class="myClass" title="bar">Works</div>';
$subst = "$1";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php