Objective: The purpose of this study was to report a novel technique, laser atrial septotomy, for the in utero treatment of hypoplastic left heart syndrome with intact atrial septum. Study design: In utero atrial septotomy by Neodymium-YAG laser photofulguration in a fetus with hypoplastic left heart syndrome (HLHS) and intact atrial septum was performed at 30 4/7 weeks of gestation. Percutaneous fetal cardiocentesis was performed to guide a contact (Neodymium-YAG) laser fiber into the right atrium with the objective of creating an interatrial communication by photofulguration of the septal tissue. Results: New onset of blood flow from the left to the right atrium was confirmed by color Doppler imaging during the procedure. The neoatrial septal defect remained patent until delivery. A 3400-g neonate was born by spontaneous vaginal delivery at 37 weeks of gestation. A first stage Norwood procedure was performed on the first day of life and surgical correction of an obstructed right pulmonary vein at 3 months. Although pulmonary vascular resistance was normal at cardiac catheterization at 2 months of age, the infant died at 5 months of age from multiple organ failure. An autopsy was declined. Conclusion: In utero laser atrial septotomy is feasible. Further experience is necessary to determine the risks and benefits of this technique for the treatment of fetuses hypoplastic left heart syndrome with intact atrial septum. Objective: The purpose of this study was to report a novel technique, laser atrial septotomy, for the in utero treatment of hypoplastic left heart syndrome with intact atrial septum. Study design: In utero atrial septotomy by Neodymium-YAG laser photofulguration in a fetus with hypoplastic left heart syndrome (HLHS) and intact atrial septum was performed at 30 4/7 weeks of gestation. Percutaneous fetal cardiocentesis was performed to guide a contact (Neodymium-YAG) laser fiber into the right atrium with the objective of creating an interatrial communication by photofulguration of the septal tissue. Results: New onset of blood flow from the left to the right atrium was confirmed by color Doppler imaging during the procedure. The neoatrial septal defect remained patent until delivery. A 3400-g neonate was born by spontaneous vaginal delivery at 37 weeks of gestation. A first stage Norwood procedure was performed on the first day of life and surgical correction of an obstructed right pulm onary vein at 3 months. Although pulmonary vascular resistance was normal at cardiac catheterization at 2 months of age, the infant died at 5 months of age from multiple organ failure. An autopsy was declined. Conclusion: In utero laser atrial septotomy is feasible. Further experience is necessary to determine the risks and benefits of this technique for the treatment of fetuses hypoplastic left heart syndrome with intact atrial septum.