Eeeeehh... Why does an attacking perm look like a heart?
Other than that, giving Life a momentum-like solution to shield problems is good and noble, however this is stronger than momentum in a few ways, even though momentum remains the supreme anti-shield thing in existence:
-It automatically uses your strongest creature's attack and increases it by a factor of 100%
-If that creature dies the next strongest will be multiplied just as much again
-The damage increase from this (especially if many are in play) is comparable to a Skyblitz per turn, depending on how attack damage is distributed among your creatures.
For these reasons, i second the suggestion of raising cost to match Parallel Universe.