Crown editorial director Steve Ross has signed journalist Charles Siebert to do a book with the working title The Heart Book: Between the Pump and P try, for 1999 publication. Siebert will further explore the issues he raised in a much-read New York Times Magazine piece about the hot topic of whether the heart is more of a memory center than supposed -- a concept also explored in Claire Sylvia's A Change of Heart: A Memoir, coming from Little, Brown this May, and in Dr. Paul Pearsall's tentatively titled Psychology of the Heart, recently acquired by Broadway Books and planned for next spring.