Detectives from the Met's Roads and Transport Policing Command are appealing for witnesses following a fatal collision in Hounslow.
Police were called by the London Ambulance Service at approximately 18:40hrs on Saturday, 7 January to reports of a motorist taken unwell in Worton Road at the junction with Farnell Road in Isleworth.
At this early stage of the investigation, it is believed that the motorist collided with an oncoming light coloured, possibly silver, VW Golf before coming to a stop in a hedge.
The male driver, aged 73, was taken to a west London hospital where he died on Sunday, 8 January.
His next of kin have been informed. A post-mortem will be held in due course.
The driver of the VW Golf briefly stopped at the scene before driving away.
Detectives would like to speak with this driver, or anyone else who witnessed the collision.
Detective Sergeant Andy Russell from the Met's Roads and Transport Policing Command said:
"I would urge anyone who witnessed the collision to contact us. We are particularly keen to speak to the driver of the VW Golf to help assist us with our investigation."
Anyone with information is asked to contact the Serious Collision Investigation Unit on 020 8543 5157 or via 101 and @MetCC.
No arrests have been made. Enquiries continue.