Silva, who lasted four batters on Sunday against the Rockies before he was lifted, said this isn't the first time he's experienced a quick heart rate but thought the problem was simply game-related adrenaline.
"There needs to be some evaluation and tests done instead of putting some sort of quick timetable and everyone saying, 'When is he going to pitch?'" Cubs acting manager Alan Trammell said Monday. "At no time was he ever in any life-threatening situation."
Silva, 31, remained in Denver overnight Sunday and flew back to Chicago on Monday afternoon. He will be examined by specialists, including Chicago cardiologist Mark Upton.
What happened at Coors Field on Sunday?
"When I was throwing my bullpen, I was feeling like my heart was beating very fast," Silva said.
Assistant athletic trainer Ed Halbur went to the mound after Silva faced two batters, but the pitcher stayed in the game. After Silva allowed hits to the next two batters, Cubs catcher Geovany Soto signaled to the dugout and head trainer Mark O'Neal went to the mound, and Silva was pulled.
"That's the last thing you want to do is come out of the game," Silva said, trying to spare the overworked bullpen from another long day. "Before, when that happened, I'd take deep breaths and try to calm down and that's what I had in my mind, is if I did that, I'd be fine. It kept getting worse and worse."
The Cubs' medical staff was unaware Silva had heart issues before, but it could be because Silva was able to get it under control. He's also experienced the increased heart rate in non-game situations.
"I always thought it was something like adrenaline or being anxious being in the game," he said. "The thing was it always went away."
But on Sunday, his heart rate didn't calm down and Silva was taken by ambulance to a Denver hospital.
"It was a very scary moment," Silva said. "I was feeling bad, but when they put me in the ambulance, I think it was the first time I ever put my family before baseball. The only thing I could think of was my kids, my family. It's very tough to be in that situation."
What the team's medical staff wants to do now is determine what the problem is so Silva doesn't have to worry the next time he takes the mound. The Cubs selected right-handers Thomas Diamond and Casey Coleman from Triple-A Iowa on Monday to fill in a gap in the bullpen and also a rotation spot Tuesday. The Cubs have an off-day Thursday, and Coleman could start in Silva's spot.
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.