A 62-year-old woman is recovering in hospital after being found with no pulse outside Woolwich DLR station on Wednesday.
Two police officers, PC James Brown and PCSO Dan Piper, were alerted to the woman, who had also stopped breathing, and began resuscitating her until London Ambulance staff took over.
Doctors and paramedics say the officers actions saved the woman’s life.
The woman is believed to have suffered a heart attack and is now recovering in hospital.
PC Brown, 37, a children’s entertainer before joining the Met 10 years ago, said: “In these situations the adrenaline just kicks in and you know that whatever you do next can make a huge difference to someone and their family. The training just kicks in.
“We were relieved when we felt a slight pulse after the CPR and we both knew we had done our best.”
He added: “This incident just makes the job worth it. If I retire in 20 years and I have done nothing else, I will always remember the day I tried my level best to give someone a chance to live.”
Former builder PCSO Piper said: “I cannot describe it how it feels when someone thanks you for saving them and when you feel you have made a difference for an entire family.”
The officers are both part of the Greenwich Transport Hub Team.
Greenwich’s borough commander Chief Superintendent Richard Wood said: “This is the Met at its finest. I am very proud. We wish the woman in question and her family all the very best for the future.”