Three patients with severe pulmonary hypertension underwent palliative atrial septostomy by dilating the interatrial septum with valvuloplasty catheter-balloons. In two cases successful dilation improved cardiac index and symptoms of cardiac failure (13 and 11 months follow-up). One patient died immediately post-septotomy due to severe hypoxemia. Severe pulmonary hypertension with low cardiac output and high right ventricular filling pressures has a very poor short-term prognosis. Atrial septostomy is a useful palliative procedure and can serve as a bridge to heart and/or lung transplantation. It is not free of risk and the resultant systemic hypoxemia can lead to dead; that is why we recommend progressive balloon diameters, stopping the procedure when improvement of cardiac index is achieved with the minimal systemic oxygen desaturation.