PORT ST. LUCIE, Fla. -- Pedro Feliciano pushed himself through rehabilitation from major surgery on his left shoulder. He willed himself through a stint in winter baseball so he could arrive here to compete for a spot in the Mets' bullpen.

But as the rest of his teammates jogged onto the field for workouts Saturday, Feliciano stayed in the clubhouse, where he pondered what will come next after doctors discovered an irregularity in his heart.

"It's hard to step back now and stay in here," said Feliciano, who returned to camp after being sent to New York for a follow-up exam. "But we'll see what happens."

Feliciano will be fitted with a heart monitor and doctors will review the data to decide what comes next. Until then, Feliciano is shut down indefinitely.

"He has a heart condition that could possibly be very serious," Mets manager Terry Collins said. "That's why we're being very, very careful with him."

General manager Sandy Alderson is expected to address the situation Sunday.

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Feliciano once was a workhorse lefty for the Mets, but his career has been derailed by shoulder problems that cropped up in 2011 with the Yankees. He hasn't made a major-league appearance since 2010.

Throughout his comeback attempt, Feliciano said he never felt dizziness, fatigue or any other sign of a heart problem. Had doctors not reviewed his physical, Feliciano said he wouldn't have suspected any issues.

"I'm surprised," he said. "Hopefully, it's nothing bad, just a different [heartbeat], that's it."