In the spirit of the Five Point Palm Exploding Heart technique and the Hokuto Hyakuretsu-ken from Fist of the North Star here is a feat and additional 9th level maneuver for Shadow Hand.

Heart Seeking Shadow:
When you use the Five-Shadow Creeping Ice Enervating Technique you have greater control over the flow of destructive ki through your target.
Prerequisites: Five-Shadow Creeping Ice Enervating Technique.
Benefit: When you use any Shadow Hand strike which allows a saving throw the DC is increased by 1.
In addition when you use Five-Shadow Creeping Ice Enervating Technique you may add or subtract 4 from the d20 roll used to determine where you hit (you may not reduce the result to less than 1 or increase it to higher than 20).

Exploding Heart Technique
Shadow Hand or Darting Viper (Strike)
Level: 9th.
Prerequisites: Five Shadow Hand maneuvers or Five Darting Viper maneuvers.
Initiation Action: 1 standard action.
Range: Melee action.
Target: 1 creature.
Duration: 2 rounds.
Saving Throw: Fortitude partial.
You strike the foe in the chest, hitting their pressure point and creating an embolism in their body which travels to their heart before bursting causing a heart attack in the target.
As part of this maneuver make a melee attack. This attack deals +6d6 damage and if you hit a living creature they must make a Fortitude save (DC 19 + your Wisdom modifier if learned as a Shadow Hand maneuver, or 19 + Int if a Darting Viper) two rounds later or die. If they succeed the saving throw they receive 10d6 additional damage.