Bubble Hearth refers to a paladin who escapes PvP, or any other type of combat, by using Divine Shield and then their Hearthstone — generally viewed as a cowardly act and those who use it often mocked for doing so. Currently, the only current ways to stop this after the paladin has cast Divine Shield is the Mass Dispel spell from a priest of level 70 or higher or a warrior's Shattering Throw ability or of course, High Overlord Saurfang's cleave.
Of course, this tactic must be used when necessary, such as when a roaming paladin finds himself unfairly situated against multiple foes and does not stand any chance of emerging victorious. This is more of a smart move than a cowardly one. It would even be possible to say that the individuals attacking the paladin are cowardly for only taking him/her on when en masse.
Also, a fortune by Sayge tells: "Divine Shields and Hearthstones do not make a hero heroic."
There is even a song made by players relating to this act:
I'm a little paladin, short and stout. Here's my hammer and here's my trusty mount. When I get in trouble I scream and shout, then I bubble and hearthstone out!
It is generally agreed that the transportation of Dalaran to Northrend was the most epic Bubble Hearth in WoW history.
Starting with Patch 4.0.1, the duration of Divine Shield was reduced to 8 seconds, whereas the casting time of Hearthstone remains at its previous duration of 10 seconds, bringing an end to bubblehearthing.