The incident took place shortly after 8:00 p.m. inside the Xanadu Sports Bar located at 6th and Clearfield streets.
Police say a quarrel culminated with a man in his 20s being stabbed in the chest.
Responding officers, originally responding for the report of a shooting, discovered the man had actually been stabbed.
Police rushed the man to Albert Einstein Medical Center where he is critical, but stable.
No arrest have been made.