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Actor Henry Winkler took the witness stand Wednesday in a lawsuit over the death of actor John Ritter, telling jurors he had a conversation with his friend just hours before he died.

Winkler, who played The Fonz on "Happy Days," also gave the jury a testimonial to the comedic brilliance of Ritter, who was best known for the classic sitcom "Three's Company."

"He kept everyone laughing. He was a professional," Winkler said.

Ritter, at the time starring in the TV show "8 Simple Rules ... For Dating My Teenage Daughter," died Sept. 11, 2003, after suffering a tear in his aorta, known as an aortic dissection. He was 54.

Winkler testified that on the day of Ritter's death he was doing a guest appearance on "8 Simple Rules" and he did not suspect anything seriously wrong with his friend.

At one point, he said, they were recalling old times before they were due to perform an episode in which Winkler was to play Ritter's new boss.

"We were reminiscing," Winkler said. "He was sweating (and said) 'I really need to get some water.' I said 'I really need to memorize my lines.' And he went one way and I went the other. And that was the last time I saw him."

The lawsuit says Ritter was treated for a heart attack instead of the aortic dissection and seeks $67 million from a radiologist who earlier gave Ritter a body scan and the cardiologist who treated him that day. The trial follows settlements with Providence St. Joseph Medical Center in Burbank and other medical personnel for about $14 million.

Defense attorneys have told the jury that neither doctor was responsible for Ritter's death and that the body scan two years earlier showed his aorta was of normal size and there was no sign it would dissect.

Winkler said that a while after he saw Ritter the members of the cast were told to go home but weren't told what was wrong. He said he knew it was the fifth birthday of one of Ritter's children and thought perhaps he had decided to quit early to celebrate.

"At 9 at night I was called and told he was in the hospital and at 11 or 11:30 I was called to say, 'We have lost John,"' Winkler testified.

He told jurors Ritter had been thrilled that "lightning had struck again" and he had a new hit show.

"He loved everyone in the cast, and they loved him," he said.

Much of Winkler's testimony dealt with Ritter's devotion to his wife, Amy Yasbeck, and his four children.

Asked what he thought the children would miss most about their father, Winkler replied: "His passion for life. His excitement for being on the Earth."

"Any conversation we had wrapped around his children, the pride and the love," Winkler said.

Ritter and Yasbeck "were an incredible team. ... They were like two sides of a whole," Winkler said.

Yasbeck wiped her eyes several times during Winkler's testimony.

Outside court, Winkler talked to reporters but would not comment on whether he believed the doctors were to blame.

A renowned expert on thoracic aortic disease said in testimony after Winkler's that the cardiologist, Dr. Joseph Lee, caused Ritter's death by providing substandard care.

Dr. John Elefteriades, chief of cardiothoracic surgery at Yale University and Yale-New Haven Hospital, said he had never before given such harsh testimony against a cardiologist.

"It's very difficult for me, and I'm here with a very heavy heart," he said. "But for one tragic decision, Mr. Ritter would have been alive. I couldn't find a way to justify the events."

The tragic decision, he said, was Lee's judgment that Ritter was having a heart attack and needed to be rushed into treatment. He said that had a chest X-ray been immediately taken, the tear in Ritter's aorta would have been found and he could have been taken to surgery.

Defense attorney Stephen C. Fraser attacked the expert on cross-examination, suggesting he was biased because Ritter's wife had recently spoken at a symposium arranged by Elefteriades and dedicated to the memory of Ritter.

The defense was expected to call its own experts on the disease.