A Minnesota company stopped all implants of a fairly new type of heart valve yesterday because the silver coating intended to reduce heart infections may occasionally cause the valve to leak.

St. Jude Medical Inc. recalled inventories of St. Jude's heart valves with Silzone coating that have not yet been implanted into patients.

Valves already implanted and the popular St. Jude's valves that do not contain the silver coating were not recalled.

About 36,000 of the silver-coated valves have been implanted into patients worldwide, including 12,000 in the United States. But St. Jude Medical said the incidence of leakage, although higher than in older heart valves that are not silver-coated, was not high enough to recall implanted heart valves.

Any patient who has a Silzone-coated valve should merely continue to get regular monitoring from a physician, the company said.

Patients should not panic at the announcement, the Food and Drug Administration agreed.

The leaks are rare, said FDA medical device chief David Feigal. Also, they typically are slow to develop, so physicians who are properly monitoring heart valve recipients have time to spot a leak and arrange for a valve replacement, Feigal said.

However, a St. Jude spokesman declined comment on whether the company would provide new valves for patients needing replacements. He noted that about 1 percent of all heart valves leak, while the incidence with silver-coated valves appears to be about 2 percent.

Silzone-coated heart valves hit the market in Europe in 1997 and in the United States in 1998, Feigal said, calling them identical to older St. Jude's heart valves except for the silver coating. Silver can have antibiotic properties, so the theory was that silver-coated valves would lead to fewer heart infections, a serious risk for all heart valve recipients, he said.

But the FDA let St. Jude sell the Silzone-coated valve even while it was trying to prove the infection theory by performing a strict clinical trial comparing patients with old valves and new valves.

That study last week turned up the leakage problem, which routine monitoring by hospitals and the FDA had not uncovered because the leaks were so rare.

Out of almost 800 patients enrolled, doctors had to remove eight leaking silver-coated valves but just one leaking noncoated valve.

Safety monitors last week decided to stop the trial, and St. Jude recalled Silzone valves still on hospital shelves.

"This experience is a cautionary tale," Feigal said, noting that no previous research had suggested such a simple valve change could have any ill effect.