The word heartlessly is playable in Words With Friends™, no blanks required. Because it is longer than 7 letters, you would have to play off an existing word or do it in several moves.
Words With Friends™ Letter Score: 17
Highest Scoring Words With Friends™ Plays In The Letters heartlessly
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Seven Letter Word Alert: (54 words)
alertly, artless, earless, earthly, elaters, essayer, eyelash, halters, hatless, healers, hearses, heaters, lashers, lathers, lathery, leasers, leashes, leather, lysates, rashest, rayless, realest, reheats, relates, resales, reseals, reseats, resells, restyle, retally, retells, sealers, seaters, sellers, sheerly, sheller, shelter, shyster, slasher, slaters, slather, slayers, stayers, stealer, stellar, stylers, tealess, teasels, teasers, tellers, tersely, thralls, trashes, yellers