Jerusalem ? Doctors next month will seal a small hole in Ariel Sharon’s heart that they said Monday led to his recent mild stroke, an announcement that drew further attention to the Israeli prime minister’s health as he campaigns for a third term.

The procedure to seal the hole will almost eliminate the risk of a stroke similar to the one Sharon suffered on Dec. 18, said Dr. Haim Lotem, head of cardiology at Jerusalem’s Hadassah Hospital. Doctors said the hole measuring less than an eighth of an inch, which allowed the stroke to happen, is a birth defect found in 15 percent to 20 percent of the population and often goes undiscovered.

“From our experience, this is something that is only a minor birth defect. It doesn’t need to be treated unless it causes problems,” Lotem told reporters.

The 77-year-old Sharon, who is 5 foot 7 inches and weighs nearly 255 pounds, is surprisingly fit, considering his girth and age, Lotem said.

But the small hole in the partition between the upper chambers of Sharon’s heart apparently led to the blood clot that caused his stroke.

“A blood clot can find its way through such a hole through the heart in the direction of the brain and cause an event like the one the prime minister had,” said Dr. Dan Elian, an Israeli cardiologist.

The procedure has not been approved by the U.S. Food and Drug Administration, though it has been successfully performed on thousands of people of all ages worldwide.

Using a catheter inserted through a blood vessel, doctors will put an umbrella-like device over the hole to seal it, Lotem said. A small camera inserted through the esophagus will guide the doctors, he said.

If the condition is left untreated, small blood clots that usually enter the lungs and dissipate harmlessly can be forced through the tiny hole, even by a cough, and pumped to the brain, where blood vessels are narrow and susceptible to blockage, said Dr. Dan Zivoni, director of cardiology at Jerusalem’s Shaare Zedek Hospital.

He said the corrective procedure is common – four were performed at his hospital this month. If, however, it includes introducing a tracking device into Sharon’s esophagus, Zivoni said, “that would require a general anesthetic.”