Shareholders Sue Maker of Heart Valve : Litigation: They charge that Pfizer kept them in the dark about problems with a mechanical heart valve made by the Irvine-based Shiley unit.

NEW YORK —  Pfizer Inc. shareholders filed a lawsuit Monday accusing company executives of withholding information about the financial impact of defects in a mechanical heart valve made by the company’s Irvine-based Shiley Inc. unit.

Pfizer stock has been battered in recent days because of potential liabilities from defects in a heart valve product that was removed from the market after reports of malfunctions that killed patients.

The class-action lawsuit, filed in U.S. District Court in Manhattan, was brought on behalf of shareholders who purchased Pfizer stock between March 27, 1988, and last Thursday, when a House subcommittee announced that it would hold hearings on the heart valve.

The shareholders said the price of Pfizer stock tumbled after the House Energy and Commerce investigations subcommittee announced the hearings, which began Monday.

They also claimed that Pfizer, without telling shareholders, had settled numerous cases involving Shiley heart valves out of court, many for $1 million or more.

“None of the information publicly disseminated by Pfizer during the class period gave any indication of the true nature or extent of the problems experienced by the company with its Shiley heart valve,” said the lawsuit.

The suit names Pfizer Chief Executive Edmund T. Pratt Jr. and six other executives. The shareholders are seeking unspecified damages for alleged losses.

“There is no merit to the suit, and we will vigorously defend it,” Pfizer spokesman Rick Honey said. Pfizer is headquartered in Manhattan and incorporated in Delaware.

Pfizer stock, which has dropped about $14 in recent weeks in apparent anticipation of the congressional hearings, lost another 25 cents Monday, closing at $56 on the New York Stock Exchange.

The so-called 60-degree Shiley valve has been implanted in 85,000 people, including about 40,000 in the United States. The Food and Drug Administration approved the valve for U.S. marketing in April 1979, but after reports of malfunctions and product withdrawals, Shiley removed it from the market in November 1986.