What is how did festus die on gunsmoke?

In the TV show "Gunsmoke," the character Festus Haggen, played by actor Ken Curtis, died of a heart attack in the episode titled "Hard Labor." Festus collapses while performing some hard labor on Matt Dillon's farm. Despite efforts to revive him, Festus passes away, leading to a somber moment for the other characters on the show. Festus was a beloved character on "Gunsmoke" and his death was a significant moment in the series.