I am sorry to tell you that this article is historical. The new cap for lives is five. [update autumn 2013]
By unlocking Charm of Life (get 20 stars) you are entitled to buy the magic Charm of life for 99 Facebook coins. That entitle you to a permanent cap of eight lives instead of the ordinary five. But…! By being an eager bubbler, you can get one extra life(total of six hearts) at 90 stars, so bubble on my fellow witches, bubble! If you don’t have the money, do the time, haha!
At 110 Stars you get a cap of seven hearts at once.
At 250 Stars you get a cap of eight hearts at once.