KIE: The birth of Siamese twins joined at the chest (thoracopagus twins) and sharing a heart creates an ethical dilemma. Infants with conjoined hearts survive no more than a few months, and physicians must decide whether to give one child a chance at life by separating the twins and sacrificing one to give the other an intact heart. Annas reviews the ethical and legal discussions generated by the birth and treatment of thoracopagus twins at Philadelphia's Children's Hospital in 1977 and 1987. He considers most of the analogies used to justify the death of one twin to be strained. The situation becomes more complicated when there is no medical indication as to which twin has a better chance of surviving. Nevertheless, Annas concludes that the bleakness of the twins' prognosis if they remain joined justifies separation and the death of one child, despite the difficulty of developing a rationale for the act.