SAN FRANCISCO -- The Cubs called up reinforcements Monday night, adding Welington Castillo and Micah Hoffpauir after placing catcher Geovany Soto on the 15-day disabled list and first baseman Derrek Lee on the bereavement list.

Soto has not played since Friday because of a mild ligament sprain in his right shoulder. He was in Monday's lineup against the Giants but scratched after feeling some discomfort in batting practice.

Lee left the team Monday to drive to Sacramento to be with his grandfather, who was ill.

Castillo was batting .251 in 65 games at Triple-A Iowa with 13 home runs and 57 RBIs. Hoffpauir was hitting .273 with 20 homers, 32 doubles and 87 RBIs in 107 games.

The Cubs added another rookie to the bullpen Monday, recalling right-handed pitcher Marcos Mateo from Iowa and optioning right-hander Mitch Atkins to the Minor League team. Mateo, who has a 1.90 ERA in his last 20 Minor League appearances, made his Major League debut Monday and took the loss in the Cubs' 4-3 loss to the Giants.

In 25 appearances this season with Double-A Tennessee and Iowa, he was 0-1 with a 3.24 ERA.

The Cubs also will be without manager Lou Piniella for this four-game series. Piniella flew to Tampa, Fla., on Sunday night to be with his mother, who was ill.

"It's been a tough year for him, but I was hoping to see him and get a chance to talk to him," Giants manager Bruce Bochy said. "I know this is his last year. I like Lou a lot and respect him and have gotten a chance to know him quite well and he's a good man."

Silva has successful cardiac procedure

SAN FRANCISCO -- Cubs pitcher Carlos Silva underwent a successful cardiac ablation at Northwestern Memorial Hospital on Monday in Chicago and is expected to pitch again this season.

Silva, who came out of his last start Aug. 1 because of an abnormal heart rate, had a procedure known as radio frequency catheter ablation performed to prevent recurrence of his paroxysmal supraventricular tachycardia.

The procedure lasted approximately two hours and was performed by Dr. Bradley Knight.

Mark DeRosa underwent the same procedure in Spring Training 2008 when he was a member of the Cubs.

"The only reason you have to take it easy is not so much the heart but where the catheter goes in and they want to make sure that's healed," said DeRosa, now with the Giants.

"It's definitely scary," DeRosa said. "I think the toughest thing [Silva] will have to get over is mentally that feeling, 'Is it ever going to come back?'"

DeRosa, sidelined following surgery on his left wrist, had heart palpitations since he was in high school. Silva thought his problems were caused by adrenaline in games.

Since he had the procedure, DeRosa has not had any recurring heart problems.

"I think it affected everything," he said. "It changed a lot of things for me -- I felt totally different from how I used to feel. I used to have palpitations during the day. For me not to get [them] was weird."

Silva was discharged from Northwestern Memorial Hospital on Monday and sent home after a normal period of observation. The right-hander was expected to begin light activity this week and start a throwing program by early next week.

Silva's diagnostic test Monday involved having a catheter inserted through his groin area. Doctors were looking for an abnormal pathway that was causing the irregular heartbeat.

"From what Mark O'Neal, our trainer, told me, the procedure went very well," said acting manager Alan Trammell.

Silva, 10-5 with a 3.92 ERA, has been able to throw on the side at least twice since Sunday. He was pulled from his last start against the Rockies after facing four batters and placed on the disabled list Aug. 2.

"It just goes to show you that even though you're a Major League athlete, you're vulnerable, and to be careful in certain situations," Giants manager Bruce Bochy said. "I'm glad they took him out of the game when they did. It was smart on their part."

Diamond seeks improvement in next start

SAN FRANCISCO -- Thomas Diamond knows he can pitch better than he did Sunday and he'll get another chance Friday when the Cubs open a three-game series in St. Louis.

"The last game, I didn't make quality pitches and they were able to put the bat on it and get some good hits off me and it made for a short day," Diamond said of his outing Sunday against the Reds. He lasted three innings and gave up five runs on four hits and three walks, taking the loss.

He's now 0-2 with an 8.00 ERA in two starts.

"It's baseball," Diamond said Monday. "It's part of the game. You're not going to go deep every game. I had a few of those in Triple-A. It happens and I have to move on and get ready for St. Louis.

"It won't be the last time I have a rough start and it definitely wasn't the first," he said.

Cubs pitching coach Larry Rothschild gave him a few pointers Monday, stressing the need to locate his fastball. Plus, his changeup is his second pitch and he needs to make sure that's right when he finishes warmups in the bullpen. They'll do more fine-tuning Tuesday during a side session.

"It's not a matter of 'Can I pitch up here?'" Diamond said. "It's just, 'When will I pitch here?' And it's up to me to stay."

The highlight so far is that Diamond, who underwent Tommy John surgery in March 2007, has had no problems health-wise this year.

"That's taken a lot off my mind," he said. "Now I just have to go out and put some things together and throw five, six, seven innings together in a row."