Hart, who was sacked by Portsmouth earlier this season, was the sixth boss, not including caretakers, of owner Flavio Briatore`s two-and-a-half year tenure at Loftus Road.
The 56-year-old had been installed until the end of the season but now leaves the club after less than a month.
Some reports suggest the decision came after Hart fell out with the Rangers board over transfers, while an argument with on-loan midfielder Adel Taarabt has also been reported.
It is thought assistant manager Mick Harford will take charge until the end of the campaign.
Source: PA
Source: PA