Vizcaino, whom the Cubs acquired from the Colorado Rockies for Jason Marquis, had not allowed a run in 3 2/3 innings over four games.
"We needed a roster spot and somebody in the bullpen had to go and unfortunately for Luis, it was him," Cubs manager Lou Piniella said. "We have some good young arms out there now and we'll go with that."
Vizcaino was the highest-paid Cubs reliever, and owed $3.5 million this year. On April 5, the Cubs released right-handed reliever Chad Gaudin, who was owed $2 million.
Samardzija struck out five over six innings in his last start for Iowa. Last year, he was called up to the big league team on July 25, and used strictly in relief, compiling a 2.28 ERA in 26 games.
"This is where you want to be," Samardzija said. "I'm excited, and hopefully the weather will start to turn around and stay nice and we'll make a good run here."
The right-hander had competed for the vacancy in the rotation this spring, which was won by Sean Marshall.
"Spring Training was a little weird because I didn't start the way I wanted to," Samardzija said. "I'm the kind of guy who likes to have results and have results quick. When I came out and struggled early in the first couple starts, I went into save mode after that and patched together a few starts. I'm not the biggest fan of Spring Training anyways. I'm ready for the season to start. Once the season got going, everything fell into a nice groove and all the stuff I was working on in Spring Training came together."
Eventually, the right-hander would like to settle on one role.
"Maybe in four years -- that'd be nice," Samardzija said. "Right now, I'm not too worried. I can be versatile with this team and help them out. That's good enough."
At Iowa, he was able to stretch his arm out and throw 60-75 pitches. Plus, he's been able to refine his pitches better. His splitter now is a setup pitch, and his slider is coming along.
"I don't think we're quite there yet," he said, "but getting up here pitching against these guys will help out a lot with the development of those pitches."
Samardzija is hoping that's the last time he'll be in Des Moines.
"As far as I'm concerned, you can 'X' it off the map," Samardzija said. "It's a great town, I don't want to put it down, but if you have to put Des Moines and Chicago on a scale, I think it tips heavily to one side."
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.