The Collaborative International Dictionary of English v.0.48:

False-hearted \False"-heart`ed\, a.
   Hollow or unsound at the core; treacherous; deceitful;
   perfidious. --Bacon. -- False"-heart`ed*ness, n. --Bp.
   Stillingfleet.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

50 Moby Thesaurus words for "falsehearted":
   Machiavellian, ambidextrous, artful, calculating, chiseling,
   collusive, covinous, crafty, crooked, cunning, deceitful,
   dishonest, disingenuous, double, double-dealing, double-faced,
   double-minded, double-tongued, doublehearted, duplicitous,
   faithless, false, false-principled, finagling, forsworn,
   fraudulent, furtive, guileful, indirect, insidious, insincere,
   perfidious, perjured, scheming, sharp, shifty, slippery, sneaky,
   surreptitious, treacherous, trickish, tricky, two-faced, uncandid,
   underhand, underhanded, unfrank, unsincere, untruthful, wily