if it's a laptop without a number pad it can be a pain as they all work slightly differently.
you either have to turn on the virtual number pad so the L key becomes a 3 or find out what key will make the L produce a 3 when you hit it. then hold down that key and left ALT and press and release the L then the other 2 keys
How big do you want the heart. If the same size as type go to INSERT then choose SYMBOLS choose ARIAL then Miscellaneous dingbats and the solid heart is there. If a large heart is wanted make sure the drawing toolbar is showing choose AUTOSHAPES then BASIC shapes