The earlier data, released in November on 104 high-risk patients implanted using the transapical approach through the ribs, showed traditional open-heart surgery produced better results.

Data for an additional 822 patients, presented Monday at a meeting of the Society of Thoracic Surgeons, showed lower mortality rates than for the original Sapien group. Mortality was 8.2 percent at 30 days and 23.6 percent at one year in the larger group, compared with 8.7 percent at one month and 29.1 percent at one year for the earlier group, Edwards said.

"It is encouraging that, in this much larger group of patients treated with transapical valve replacement, investigators observed a trend toward patients feeling better faster and having improved outcomes," Edwards Chief Executive Michael Mussallem said in a statement.

The U.S. Food and Drug Administration in November approved Edwards' Sapien valve for patients deemed too sick to have open-heart surgery.

In addition to the transapical procedure, the company has developed a transfemoral approach in which the valve is threaded to the heart via a catheter inserted at the groin.

Irvine, California-based Edwards is expected to present results from its study, called Partner, to an FDA panel this spring in hopes of gaining approval for Sapien in a wider population of patients.

"I think the Street will come away from it increasingly optimistic in Edwards' ability to get transapical past an FDA panel," said J.P. Morgan analyst Mike Weinstein in an e-mail.

Goldman Sachs analyst David Roman also predicted FDA would approve the device for a larger market.

"The bottom line is the data clear the way for full Partner A approval later this year, in our view," Roman said in a note to clients.

(Reporting By Susan Kelly; Editing by Gary Hill)

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