R. Moshe Feinstein and Tzitz Eliezer on Heart Transplants and Brain Death (1 Adar Sheni)

שו"ת אגרות משה חושן משפט ב:עב 1 Adar Sheni 5738 (1978)

To transplant a heart requires taking it out of someone in whom it's still beating. And, for a long time, didn't do that much for the recipient. What does halacha say?