A known risk of scuba diving is decompression illness, commonly known as “the bends.” The brain can be injured in decompression illness because small gas bubbles that form in the blood as a diver rises to the surface can block circulation to the brain. The symptoms of decompression illness include skin changes, joint pain, confusion, and other transient or lasting neurologic symptoms. Brain imaging tests in divers who have previously had decompression illness show areas that have been injured as a result of getting too little oxygen (ischemic brain lesions). A recent study suggested that these brain lesions also occur in divers who have never had symptoms of decompression illness. It is believed that these lesions may be more common in divers who have an abnormality of the heart called a patent foramen ovale. A patent foramen ovale is an abnormal hole in the wall between chambers of the heart, which could allow more bubbles to get into the brain circulation.