Enchanted Cards must be used multiple times before they are removed from the board. Each time you use an Enchanted Card, one of its heart-shaped potion bottles is used up. When the last potion bottle is gone, it acts like a normal card and can be removed from the board as usual.
You may use an Enchanted Card multiple times within a single word. For example, if you had an Enchanted "E", you could make BREEZE, using it three times in that word.
If you have an Enchanted Card in your letter rack, and you clear the rack, it restores one potion bottle to that Enchanted Card on the board.