The Witch’s Heart by Iris Kincaid

Margo Bailey never expected to live long enough to see her thirtieth birthday. A heart defect that she’s had since birth has taught her to live cautiously and expect the worst.
On the other hand, Lilith Hazelwood, the most powerful witch in town, expected to live a freakishly long life. But she is killed under sinister circumstances, and her precious and powerful organs are bestowed to several clueless beneficiaries, like the faint-hearted Margo Bailey. Lilith’s spirit lingers on, filled with anger, seeking vengeance.
Margo’s new lease on life does not come without complications – a local murder investigation, an old friend in need, an intriguing and persistent young cop, and some unsettling new powers. What will unfold when a timid young woman inherits the heart of a powerful witch?