FUNNYMAN Chevy Chase has ballooned to nearly 300 pounds, and the bulky star was rushed to the hospital with breathing problems that sparked fears he might be suffering from a heart attack, say sources.

A rep denies the 70-year-old “Sat­urday Night Live” legend is battling heart problems, but “Chubby” Chase recently shocked onlookers with his gut-busting paunch.

“I saw a big guy, wearing sun­glasses and a US Open cap with his T-shirt hanging over his bulging belly,” recalled an eyewitness who spotted Chase at LAX on May 5.

“When someone said, ‘Hey, that’s Chevy Chase,’ I couldn’t believe it. He must weigh 300 pounds!”

Just 8 days earlier, the 6-foot-4 former star of NBC’s “Community” had trouble breathing and was rushed to an L.A. hospital with a possible heart attack.

“The emergency room doc­tors and nurses were scrambling around like crazy, telling him to lie down so they could get his vital signs,” said the source.

But Chase insisted that he couldn’t stay because he had to catch a plane to New York, said the source, adding: “The ER staff was trying to help him, but it seemed he was barely cooperating. In fact, he was giving them a hard time.” At one point, Chase – star of the classic film comedy “Caddyshack” and the “National Lam­poon’s Vacation” flicks – was told he might risk his life if he left.

“But Chevy kept saying he was fine, and he needed to go,” said the source.

When doctors saw his test results several hours later, Chase – who entered rehab to beat an addiction to prescription painkillers in 1986 – was allowed to leave.

“But for a time it seemed like a grave situation,” noted the source.

A rep for the actor – who lives in Bedford, N.Y., with third wife Jayni, 56, mother of his three adult daugh­ters, aged 25 to 31 – pooh-poohed talk of a heart attack. Chase’s visit to the emergency room “was an asthma attack” and “had nothing to do with his heart,” the rep said.

But a second source warns that Chase’s expanding waistline could trigger a medical crisis.

“You have to worry what all that ex­tra weight might be doing to Chevy’s health,” said the source. “Being so overweight can lead to heart problems, not to mention diabetes and a bunch of other potentially deadly conditions. Chevy used to be a good-looking guy, but he seems to have let himself go. It’s sad.”