"Dr. Lee said, 'No, there's no time. You're in the middle of a heart attack,'" Yasbeck testified.
She said Lee asked Ritter to sign a consent form and read him its details.
Asked by her lawyer, Moses Lebovits, what happened next, Yasbeck broke into gasping sobs.
"I leaned down to John's ear and said, 'I know you're scared but you have to be brave and do this because these guys know what they're doing.' And he was brave for all the time I saw him," she said.
Yasbeck said that as Ritter was wheeled down a hall on a gurney he used sign language to say "I love you." She said she mouthed the same words back.
"He went around the corner and that's the last time I saw him," she said.
Ritter, 54, fell ill earlier in the day while working on the sitcom "8 Simple Rules ... for Dating My Teenage Daughter" and died of a torn aorta at Providence St. Joseph Medical Center in Burbank. His family is suing Lee and a radiologist, Dr. Matthew Lotysch, who did a body scan on Ritter two years earlier, for $67 million.
The doctors deny wrongdoing. The radiologist has testified the aorta was normal in the scan but Ritter had coronary artery disease at a relatively young age.
Yasbeck told of the long wait to hear what was happening after Ritter was wheeled away, and of overhearing someone calling "code blue," which she recognized from an audition she had done for the show "ER."
Shortly after that, she said, a doctor who had arrived from the Disney studios came out and told her Ritter was "crashing" and that a surgeon had been summoned.
She said the doctor drew a picture for her and explained that Ritter's aorta had shredded and "it was a bad thing."
At some point — after she was joined by Ritter's ex-wife, Nancy Ritter, and their son Jason — the surgeon came to them.
"He said it was over and John's dead, that they worked on John for a long time but the damage was done by the time he got there. It was a fait accompli and John was dead," Yasbeck said.
Yasbeck then told of going home to tell her 5-year-old daughter, Stella, that her father had died. She waited until the next morning because the child was asleep.
Asked by her lawyer to tell jurors what Stella lost with Ritter's death, she said, "As much as I lost my husband and the love of my life and my soul mate, what I lost was Stella's father."
She said when it came to child rearing, "I really was dependent on him. I was 36 years old. He was so freaking wise about this stuff. And Stella, every day she wakes up and there's a new way to miss her father. I can't make up for that. It's a new road to face every day."
The testimony was offered in part to demonstrate to jurors the devastation suffered by the family from the loss of Ritter. In the courtroom audience, his brother, Tom, wiped his eyes.
Nancy Ritter, who was married to the actor for 19 years, also took the stand and testified about his importance to their three children and his decision to have a complete body scan two years before he died.
She said she urged him to do it and when it was over he told her it had gone well.
"He implied to me that he was reassured he was OK. Maybe he was protecting me," she said.
The plaintiffs rested their case after Yasbeck's testimony and the defense opened its presentation with a brief appearance by Ritter's personal trainer, who said the actor was concerned about improving his health and was working out regularly.
The current lawsuit follows settlements with the hospital and eight other medical personnel for about $14 million.