Former President Bill Clinton is headed back to the hospital for a procedure to remove fluid and scar tissue from the left side of his chest. The procedure will correct a fairly rare complication resulting from the open-heart surgery he underwent in September.

Dr. Allan Schwartz, chief of cardiology at New York-Presbyterian Hospital, Columbia University Medical Center, says Mr. Clinton passed a stress test with "flying colors" before he embarked on a recent trip to areas of Asia devastated by the tsunami. But Dr. Schwartz says the former U.S. leader was becoming increasing short of breath during routine exercise.

"President Clinton has been following an increasingly active exercise program and is exercising up to six to seven days walking on four miles on hills in Chappaqua when he is home," he said. "He has noticed over the past month or so on steep hills he was getting winded a bit more easily. At the same time he was starting to feel a bit of discomfort in his left chest - nothing severe but a bit of discomfort. The combination of those two things, along with changes both in his physical examination and his X-ray led to our decision to recommend this procedure."

Dr. Schwartz says the procedure, called decortication, is not "medically urgent." The purpose is to remove scar tissue caused by a build-up of fluid and inflammation, resulting in compression and the collapse of the lower lobe of Mr. Clinton's left lung. The procedure will be performed either by inserting a tiny video-assisted thorascope between the ribs or by making an incision.

Mr. Clinton, who is 58 years old, leads an active life, traveling extensively. A hospital spokesperson says the former president should be able to resume his work without limitations once he has recovered. He is expected to be in the hospital for three to 10 days.