<div width="250" height="123" title="" style="margin-top: -5px;></div>preg_replace('/<div.*?height="(.*?)".*?>(\/?)>/i', '<$1$2>', $string);
$regexp = '/<div.*(height="[\d]+")[^>]*>(.+)/i';
var_dump(preg_replace($regexp, '<div $1>$2', $string));