The attack happened around 1:00 a.m. inside a home on the 5100 block of James Street in Philadelphia's Frankford section.
Police say the victim was actually trying to break up an argument between a man and a woman. That's when, they say, the man grabbed a sword and repeatedly stabbed the victim's left arm.
Police now say the victim may lose that arm.
The woman drove the victim to the hospital where he remains in critical condition.
The suspect, who was known to the victim, fled the scene and remains on the loose.