More than two decades after John Ritter’s sudden death, his widow, Amy Yasbeck, is revealing new details about his final hours and the medical misdiagnosis she says contributed to the beloved actor’s death.

Ritter, best known for playing Jack Tripper on “Three’s Company,” died in September 2003 at just 54 years old. He suffered an acute aortic dissection, a life-threatening tear in the inner layer of the aorta, the body’s largest artery.

But when Ritter arrived at the hospital with chest pain, doctors initially believed he was having a heart attack.

“John was sadly misdiagnosed on the night he passed away,” Yasbeck told Fox News Digital.

Yasbeck said doctors did not perform imaging before treating Ritter for a heart attack. Because of his age, weight and symptoms, she said he appeared to fit the profile, and doctors began giving him blood thinners.

The problem was that Ritter wasn’t suffering from a blockage.

“It was the opposite,” Yasbeck explained. “It wasn’t a block in his heart, it was a tear in his aorta, so everything they did that night led to what eventually happened.”

Yasbeck said quickly recognizing an aortic dissection can make a critical difference.

“There are ways, once it starts dissecting, if you get to the hospital in time, your chances are way better of living,” she said.

Following Ritter’s death, Yasbeck filed a wrongful death lawsuit alleging his condition had been misdiagnosed. In 2008, a jury found in favor of the two physicians remaining in the case.

Ritter’s death also revealed a troubling pattern in his family.

Doctors now believe his father, country music legend Tex Ritter, may have died from an undiagnosed aortic dissection. After John’s death, screening discovered the same condition in his brother Tom, allowing him to undergo surgery before it became fatal.

Ritter’s son Tyler now receives annual screenings and makes sure his children understand their family history.

“Our mission is that he is the last in our family to suffer a dissection,” Tyler said.

The family has also turned Ritter’s death into a mission through the John Ritter Foundation for Aortic Health, which Yasbeck founded to raise awareness about aortic aneurysms and dissections.

More than 20 years later, Yasbeck has seen signs that her husband’s story is making a difference.

She recalled recently taking a friend with chest pain to a hospital. Without knowing who she was, medical staff told Yasbeck they were ordering a CT scan to check for “the John Ritter thing” and rule out an aortic dissection.

Yasbeck said hearing those words brought a sense of relief.

“There was kind of a pre-John Ritter awareness of aortic dissection and a post,” she said. “Sadly, John died in the last hours of pre-John Ritter awareness.”

For Tyler, his father’s death remains painful, but knowing his story may have protected other families has provided what he called a “massive silver lining.”

“It is unfortunate. It’s a tragedy,” Tyler said. “But it has happened. And, as a result, there are just countless numbers of lives that have been saved.”