Sen. Bernie Sanders, 78, was hospitalized in Las Vegas, Nevada.

"During a campaign event yesterday evening, Sen. Sanders experienced some chest discomfort. Following medical evaluation and testing he was found to have a blockage in one artery and two stents were successfully inserted," said Sanders’ senior adviser Jeff Weaver on Wednesday in a statement.

"Sen. Sanders is conversing and in good spirits. He will be resting up over the next few days," Weaver said. "We are canceling his events and appearances until further notice, and we will continue to provide appropriate updates."

ABC News first learned from officials about the Vermont senator being hospitalized after his plans to attend a presidential gun forum changed.

He is one of three septuagenarians in the Democratic primary, and the oldest. Former Vice President Joe Biden is 76. Massachusetts Sen. Elizabeth Warren is 70.

President Donald Trump, who was the oldest elected president, is 73. If elected, Sanders would be the oldest president to serve.

Sanders' last public appearance was at the Las Vegas shooting memorial on Tuesday night. Earlier this week, he was in New Hampshire where he held seven back-to-back events over the course of two days.

Shortly after announcing his presidential campaign in February, Sanders appeared on the campaign trail with a bandage on his head after being treated at a walk-in clinic for a minor injury while campaigning in South Carolina in mid-March. Sanders cut his head in the shower, according to the Associated Press, and after receiving a half-dozen stitches, the senator was given a "clean bill of health."

Scott Olson/Getty Images

On Wednesday, Sanders is currently on a campaign swing through Nevada, hosting a town hall on Medicare for All and social security in Las Vegas ahead of his appearance at the Giffords and March for Our Lives’ Presidential Gun Safety Forum on Wednesday.

The news of Sanders' hospitalization comes on the heels of the presidential contender announcing he raised a whopping $25.3 million in Q3 -- the largest quarter for any Democratic candidate this year, and a number that, on its own, eclipses Warren's entire first and second quarters' total.

Sanders entered his second bid for president, after falling short to Hillary Clinton in the 2016 Democratic primary, as a known quantity. Despite the presence of another liberal stalwart in the 2020 race, Warren, the former mayor of Burlington continues to carve out a lane for himself in a crowded field that still counts 19 with his blunt style and progressive ideals - including his signature "Medicare for All" proposal, which has been embraced by several of his Democratic rivals and often a key source of debate throughout the protracted contest.

Last month, Sanders told ABC's "The View" that 2020 is different because "many of the ideas that I talked about," including universal health care, "were perceived to be radical," but now "a lot of candidates and the majority of the American people agree."

This is a developing story. Please check back for updates.