Background: Raymond William Stacy Burr was born May 21, 1917, in New Westminster, British Columbia, Canada. His father, William Johnston Burr (1889-1985), was a hardware salesman; his mother, Minerva Annette (nee Smith, 1892-1974), was a pianist and music teacher who was born in Chicago, Illinois. Burr's ancestry included Lebanese, Irish, English, Scottish, and German. When Burr was six, his parents divorced.
Context: In 1985, Burr was approached by producers Dean Hargrove and Fred Silverman to star in a made-for-TV movie, Perry Mason Returns. The same week, Burr recalled, he was asked to reprise the role he played in Godzilla, King of the Monsters! (1956), in a low-budget film that would be titled Godzilla 1985.  "When they asked me to do it a second time, I said, 'Certainly,' and everybody thought I was out of my mind," Burr told Tom Shales of The Washington Post. "But it wasn't the large sum of money. It was the fact that, first of all, I kind of liked 'Godzilla,' and where do you get the opportunity to play yourself 30 years later? So I said yes to both of them."  He agreed to do the Mason movie if Barbara Hale returned to reprise her role as Della Street. Hale agreed, and when Perry Mason Returns aired in December 1985, her character became the defendant. The rest of the principal cast had died, but Hale's real-life son William Katt played the role of Paul Drake, Jr. The movie was so successful that Burr made a total of 26 Perry Mason television films before his death. Many were filmed in and around Denver, Colorado.  By 1993, when Burr signed with NBC for another season of Mason films, he was using a wheelchair full-time because of his failing health. In his final Perry Mason movie, The Case of the Killer Kiss, he was shown either sitting or standing while leaning on a table, but only once standing unsupported for a few seconds. Twelve more Mason movies were scheduled before Burr's death, including one scheduled to film the month he died.  As he had with the Perry Mason TV movies, Burr decided to do an Ironside reunion movie. The Return of Ironside aired in May 1993, reuniting the entire original cast of the 1967-75 series. Like many of the Mason movies, it was set and filmed in Denver.
Question: What was wrong with his health?

Answer: