State Sen.-elect Hiram Monserrate flew into a volcanic rage and attacked his girlfriend after seeing another man’s business card in her purse, sources told The Post yesterday.

The law-enforcement sources also believe that the jealous Monserrate was so angry that he deliberately broke a glass into jagged pieces so he could slash Karla Giraldo, who required 20 stitches around her left eye following the alleged domestic-violence assault.

Sources said her wound is consistent with a jagged piece of glass tearing into her skin.

Investigators have seen the business card and who it belongs to and consider it potential evidence in the case.

Meanwhile, it was revealed that a top aide to Senate Democratic Leader Malcolm Smith showed up at the police station to offer assistance to Monserrate, a fellow Democrat, on the morning he was busted.

Smith’s office confirmed that Chief of Staff Mortimer Lawrence – a former Queens assistant DA – went to the 105th Precinct station house in Queens Village to help Monserrate, but insisted Smith did not direct him to do so.

“[Lawrence] was there on his own volition to see how he could help an incoming member of the Senate,” said Smith spokesman Austin Shaffran.

“He did not do anything to try to intervene on Mr. Monserrate’s behalf. He did not speak to Monserrate at the precinct. Nor was his appearance at the direction of Senator Smith,” Shaffran said.

He added that Lawrence showed his credentials as a lawyer, not as a Senate staffer.

Critics said Lawrence’s effort to aid an accused domestic batterer was wrong.

“Give me a break. This guy is a former Queens prosecutor. This is unethical and inappropriate,” fumed state Sen. Marty Golden (R-Brooklyn).

murray.weiss@nypost.com