Police and ambulance crews were called to the scene at Greenwich High Road on Thursday night after a collision between the victim's BMW and a London taxi.
The road was closed at 8.50pm and remained shut for most of the evening while traffic police carried out their investigations.
A spokeswoman for Greenwich Police said it was believed the man had the heart attack before the collision.
"The driver of a BMW was taken ill at the wheel and his vehicle subsequently collided with a taxi," she said.
"The 55-year-old male driver of the BMW was taken to King's College Hospital suffering from what was believed to be a cardiac arrest. Temporary road closures were put in place in the area."
A spokeswoman for the ambulance service said: "We sent an ambulance crew, two single responders and a duty officer and the male patient, who was in cardiac arrest, was taken to King's College Hospital."
Source: The Wharf