Second Heart (4e Future Technique)
From D&D Wiki
With additional blood-generating and circulatory power, there's less chance for you to bleed out. In a dire situation your extra heart can go into overdrive at the risk of exploding.
Benefit: When you make a death saving throw and score 10 or higher, you are stabilized.
Overcharge: When you are dying or stabilized you can roll d20 at the start of your turn.
♦10+: You gain hit points equal to your bloodied value.
♦9 or less: You die.