Police Dog Murphy was helping his handlers search for suspects following an assault in the borough when officers stopped a vehicle in Stanley Road, Hounslow, on Saturday (April 16).
The Met's dog support unit searched the nearby area, where the German Shepherd found the huge drugs haul.
Police arrested four men aged 22 to 35 on suspicion of possessing Class A drugs with intent to supply. They have all been bailed to a date in June.
PD Murphy's exploits earned him plenty of praise after the Metropolitan Police Taskforce tweeted about his success, with several people suggested he had earned himself an extra biscuit.