A Long Island driver slashed another motorist with a boxcutter and bit his fingers in a wild, road rage-fueled burst of violence Tuesday, cops said. 

Jayson Heitner, 26, was behind the wheel of a Jeep around 3:40 p.m. when he struck a 2017 Mercedes Sprinter van heading north on West Neck Road near Old Hickory Lane in Huntington, Suffolk County Police said. 

Heitner flew into a rage and approached the 60-year-old Sprinter driver with a boxcutter in hand, leading to a physical fight, cops said. 

He then slashed the older man all over his face and body, and bit several of his fingers during the brawl, authorities said. 

The victim was taken to a local hospital, where he required immediate medical attention, including multiple stitches to close his wounds, according to the criminal complaint. 

Heitner was arrested and charged with second-degree assault, a felony, the court doc said. 

He pleaded not guilty during his Wednesday arraignment in First District Court and was ordered held on $75,000 bail, $150,000 bond or $750,000 partially secured bond.

He is due back in court on Monday.

Heitner’s attorney, Chase Brown, claimed the driver of the much-larger Sprinter hit his client’s Jeep Grand Cherokee first – and that that his client was protecting himself from the motorist, who admitted in court that he was holding a knife.

“He had a knife in his hand when my client went up to the car to make sure he was OK,” Brown told The Post by phone. “He’s the one who started it. We look forward to exonerating my client. There’s a clear self-defense claim.”

Heitner is in school to become a physician’s assistant and he is now working as a paramedic, Brown said.