James Whitey Bulger, the Boston mob boss who is awaiting trial has been treated in hospital for heart issues.

The Boston Globe reports a friend of Bulger’s said the 83-year-old was taken to a hospital recently for an irregular heartbeat. The friend claims it was at least Bulger’s third trip to the hospital since he was captured in June 2011.

Richard Sunday, who did time with Bulger in Alcatraz says he received a letter from Bulger saying he was taken to a hospital on February 12 for atrial fibrillation.

After doctors examined him he was returned to Plymouth County Correctional Facility, where he is been held until his trial. The FBI says he was responsible for at least 19 murders, his trial is due to begin on June 6th.

Read More: Whitey Bulger’s racist reaction to President Barack Obama helped lead to his capture

Sunday says Bulger wrote in his letter, "exercise is over for me" and "this is the end of the trail for me."

"So far, I've had a year and a half and a lifetime to go," he wrote.

Sunday told reporters he was concerned about Bulger’s health.

"If we are America, we're supposed to be a country of justice," Sunday said.

"A lot of people figure whatever they're doing to him, well, he's got it coming. But if you want justice, you have to give justice," he said.

"You don't lock him up in a solitary condition and give him cold food, nobody to talk to."

Bulger's lawyer, J.W. Carney Jr., told The Boston Globe that officials at Plymouth prison have been "very professional" and responsive to Bulger.

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‘Whitey’ Bulger arriving home to BostonStuart Cahill