The number of people surviving cardiac arrests outside hospital has more than trebled in the last five years.
Just under one in six people who had a cardiac arrest witnessed by another person survived during 2006/07.
This compares with a survival rate of one in 10 during the previous year, according to the London Ambulance Service (LAS) report.
The study also found ambulance staff responded to cardiac arrest call-outs a minute faster than last year.
LAS REPORT FINDINGS
The average age of a cardiac arrest patient was 67
About two-thirds of cardiac arrests in London occurred in the home
Of those that occurred in public, over a third took place in the street
Cardiac arrests occurred most frequently on a Saturday
When a cardiac arrest occurs a person's heart stops beating, they lose consciousness, stop breathing and have no signs of circulation.
Medical director Dr Fionna Moore said: "Every second is vital when someone collapses and stops breathing, and to have seen such tremendous improvements in these survival rates is a great achievement.
"There is no greater satisfaction for our staff than to know that they have helped save someone's life."