Last August, when Children’s Hospital Los Angeles cardiologists confirmed that the heart of a 27-week-old fetus suffered from a critical cardiac condition that prevented blood returning from the fetus’s lungs from circulating back into the body, they told the parents that their child faced certain open-heart surgery after birth. Even worse, babies born with this very rare condition—hypoplastic left heart syndrome (HLHS) with restrictive atrial septum—have a 50 percent neonatal mortality rate.