CHICAGO -- Carlos Silva threw 25 pitches in the bullpen on Monday, the first time he's thrown off a mound since undergoing a cardiac ablation one week ago to correct an abnormal heart rate, and was close to making a Minor League rehab start.

"It felt weird but it felt good," Silva said of his session Monday.

Silva, who came out of his last start Aug. 1 after four batters, had a procedure known as radio frequency catheter ablation (RFCA) performed to prevent recurrence of his paroxysmal supraventricular tachycardia (PSVT). The procedure was done Aug. 9.

The right-hander will have another side session Wednesday and then the Cubs medical team will determine the next step. Silva said he felt relieved after Monday's session.

"Friday was the first time I threw [and played catch]," he said. "I told the trainer I don't know if it's mental or what, but I felt like I don't have to worry about it anymore. I felt loose, that nothing is going to happen. I know nothing bad is going to happen."

The experience was a little nerve wracking, Silva said.

"For my family, it was something big and they were worried, and my wife was so worried," he said. "When you're talking about your heart, it's something big. The good thing was before I had the procedure, a lot of people talked to me and said, 'My sister had this done,' or 'My brother had this done and everything will be fine.'"

Silva (10-5, 3.92 ERA) said the medical staff told him he'll feel the difference quickly.

"[The doctor] said, 'You won't be as tired any more and this will be better for you,'" Silva said.

Worth noting

Cubs catcher Geovany Soto, on the disabled list with a sprained ligament in his right shoulder, was to begin taking batting practice on Tuesday. Soto did some work Monday with catching instructor Matt Sinatro. He's eligible to come off the disabled list Sunday. ... Starlin Castro did not start Monday, a rare night off for the rookie shortstop. He did some work with infield coach Alan Trammell prior to the game. ... They say it's tough to evaluate players in September. What about August? "You can look at their stuff, you look at their composure, you look at their mound presence, you can look at how they respond if they get roughed up a little bit," Lou Piniella said. "There are things you can look at, believe me, especially when you're playing these teams in contention and they're going after it. This is a whole lot different here than pitching in the Minor Leagues." ... The Arizona Fall League was expected to announce players participating, and one of the Cubs' candidates is outfielder Brett Jackson, the team's No. 1 Draft pick in 2009. ... Piniella was asked about the antiquated conditions at Wrigley Field but said that's not the reason the team has struggled this season. One of the upgrades was a new kitchen in the clubhouse. "They had caviar in there," Piniella said. "I told Otis [Hellman, clubhouse manager], if we were in first, they'd have a chef from France."

Lee out for next few days with back woes

CHICAGO -- Cubs first baseman Derrek Lee had an injection in the epidural of his lower back to ease discomfort from a bulging disk and was expected to be sidelined two to three days.

"It doesn't bother me swinging, just moving around on defense and trying to run," Lee said on Monday. "It gets pretty tight."

Lee has homered in three straight games for the sixth time in his career, and the first time since June 18-20 last season. However, he's hitting .251 overall. He didn't blame his back problems on his numbers this year, saying it's tough sometimes to bend over, but it doesn't affect his hitting.

Manager Lou Piniella had a little trouble explaining what was wrong prior to Monday's game.

"Derrek has a minor 'ball disk,'" Piniella said, then corrected himself. "Minor bulge disk. How about that? 'Ball disk.' I feel like a mechanic."

The problem is on the right side of Lee's lower back.

"He went to [athletic trainer Mark O'Neal] during the game [Sunday], and right away, we took him out of the ballgame," said Piniella, who removed Lee from the game as a precautionary measure.

Xavier Nady, who has hit safely in his last five starts, batting .316 with three doubles and four RBIs, started at first base on Monday in the Cubs' series opener against the Padres.