Carpenter hasn't pitched since allowing five runs in six innings of a season-opening loss to the New York Mets.

The right-hander, who went on the disabled list April 2, had arthroscopic surgery to remove bone spurs in his elbow on May 9. He developed swelling and stiffness after a rehab start for Class-A Palm Beach on July 8.

Carpenter consulted with three orthopedists before deciding to have the procedure commonly known as Tommy John surgery.

"Carp coming back was huge for us," manager Tony La Russa said Thursday, before his team played the Atlanta Braves. "If he's not coming back, you need to factor that in. But we've been a little over .500 with this group out there. The games go on."

In five postseason starts last year, Carpenter went 3-1, helping the Cardinals win the World Series with eight scoreless innings in a 5-0 victory over Detroit in Game 3. He is 51-18 with a 3.10 ERA in 93 starts for St. Louis over the last three years.

The Cardinals did not announce what day Carpenter will undergo surgery.

Before signing as a free agent with St. Louis in December 2002, Carpenter went 49-50 with a 4.83 ERA in parts of six seasons for Toronto. He missed part of 2002 and all of '03 after having arthroscopic surgery on his right shoulder.

Carpenter had bursitis in his shoulder last seasons, but went 11-6 with a 3.27 ERA in 22 starts after returning from the DL on June 6.

Only Minnesota's Johan Santana and Houston's Roy Oswalt, both with 55 wins, had more victories over the last three years.

The Cardinals also have left-handers Mark Mulder and Todd Wellemeyer and right-hander Josh Kinney on the DL. Right-hander Josh Hancock was killed in a car crash earlier this year.