You may use "HealWatch", where you can lock 'your bar', so that it is shown always to see the heals that are about to land on you:
http://www.wowinterface.com/download...HealWatch.html
Alternatively, you could look at "HealNotify":
http://www.wowinterface.com/download...fo.php?id=4994
Cheers,
Farook