One of every 150 infants (more than 32 000) is born with a structural heart defect each year in the United States. A hole or opening through the wall of tissue separating the atria (the heart's upper chambers) is called an atrial septal defect (ASD) and accounts for 10% of all congenital heart defects. There are 3 types of atrial septal defects; the most common type is called a patent (open) foramen ovale (PFO)—a small opening between the 2 atria that assists blood circulation in the fetus and is present at birth. Shortly after birth, the foramen ovale usually closes gradually. In infants with a persistent hole, there is an increased workload of the right side of the heart with excessive blood flow to the lungs. Symptoms associated with this condition (shortness of breath, fainting, and cyanosis—bluish coloring of the skin due to low oxygen levels in the blood) may be absent or so mild that they go unnoticed; 2% to 3% of healthy adults have a small PFO. The December 27, 2006, issue of JAMA includes an article on increased risks of respiratory problems and heart failure associated with a patent foramen ovale in mountain climbers.