A homeless man stabbed a good Samaritan in the chest in Queens Wednesday, after the victim attempted to break up an argument with a woman on a subway platform.

After observing the 5 p.m. altercation on the northbound F train platform at the 75th Ave. station in Forest Hills, the 49-year-old intervened, police sources said.

The homeless man responded by pulling out a knife and stabbing the victim in chest. He then fled the scene.

After making his way up the subway steps and past four storefronts, the victim collapsed on the sidewalk. The victim was rushed to Jamaica Hospital, where he is expected to survive.

The relationship between the suspect and the woman has been described as ‘unclear.’ No arrests have yet been made, sources said.