Frank Mack hardly notices his right heel bouncing off the tile floor, a throwback to years of emotional problems. It was at this same federal prison in Springfield, Mo., that Mack once underwent electric-shock therapy for manic depression.

The 51-year-old Mack is back in prison, serving a mandatory sentence of 20 months to five years after police made an undercover drug purchase and caught Mack, a lifelong drug user, with 26 appetite-suppressant pills called Preludin.

Prosecutors used his long record of petty crimes as leverage to get him to plead guilty, though Mack says dealing drugs was never his line.

"They kept talking about serving repeater papers and double the prison time if I didn't plead guilty and I didn't feel that I could beat the charge because I was really guilty," said Mack as he sat in the prison visitors' lounge, a catheter taped to his chest for the heart medication he receives daily. "I did give it to him. I wasn't even going to argue that. But I didn't sell him any drugs, as far as like a dealer. There's nothing on my record about being a drug dealer."

According to Mack, he was hanging out near 12th and U streets NW with some friends when a man called "Blue" said he wanted some of the pink pills for himself.

Mack sold him some for the discount price he had paid -- a transaction witnessed by an undercover officer -- and after "Blue" later sold one pill to the undercover officer, Mack ended up under arrest.

Mack started using heroin when he was 16 and still remembers times when he scoured the streets looking for the most potent "bomb" he could find.

He overdosed several times and tells a story about once waking up in Mount Olivet Cemetery, where a friend who thought he was dead had dumped him. He was arrested a couple of times for assault and robbery as a youth but made his career picking pockets.

Mack was sent to various federal prisons, which had treatment programs for his drug and mental problems. While at the penitentiary in Danbury, Conn., in 1977, he suffered a heart attack during a fire at the prison. He received several thousand dollars to settle a lawsuit he brought against prison authorities.

It was that money Mack said he used to fuel his days of drinking and shooting "Bam" -- the street name for Preludin. Some days he would shoot as many as 20 pills after dissolving them. He liked to visit an "oil joint" near 14th and U, where he would pay $5, lie down and close his eyes while one of the women would cook the pill and shoot it into a vein in his neck.

"I liked the way it made me feel, like I had no worries, no troubles," he said. "And I could halfway function. I used to be depressed a lot and this used to keep me from being depressed."

While Mack was waiting to be sentenced on the drug distribution charge, he was picked up again for helping a friend steal two record albums out of a car trunk. His attorney, J. Brian Molloy, asked that Mack be placed on probation, but Judge Nicholas Nunzio imposed the mandatory term.

Mack "was a pleasant fellow. He surely was not a dangerous individual," Molloy said. "As far as I could tell, he wasn't a serious threat to society, although he may have been a threat to himself."

Mack remembers the police telling him he might get off easier if he helped lock up some of his friends, but Mack refused.

"How is it going to help me?" he says. "I'm going to jail anyhow. They've got a new law passed and I'm going to jail anyhow."