The NHS is operating a policy that sees 999 calls recorded as having been responded to swiftly, even if health professionals did not attend, it has been claimed.
It has reclassified thousands of "life-threatening" calls in which the target was apparently missed, a whistleblower said.
South East Coast Ambulance Service was allegedly able to manipulate the figures by proving that public defibrillators were within 250 metres of the patient.
The paramedic whistleblower told the Daily Telegraph the policy had been applied to thousands of calls.
Ambulance services are supposed to ensure that 75% of life threatening calls are responded to within eight minutes.
According to NHS guidance about "Red 2" cases, the target can be met if a response comes from an ambulance, rapid response vehicle or a "public access defibrillator" with a person trained to use it.
But it is claimed that trusts have been allowed to consider targets as having been met if the equipment is on hand, regardless of whether the patient could have been helped by a defibrillator and no attempt was made to use it.
An NHS England spokesman said the guidance should be adhered to in letter and in spirit.
He added: "We support greater training for the public, the use of community first responders and similar schemes, and also the placement of PADs in accessible locations.
"The presence of a trained individual and a defibrillator at the scene of a cardiac arrest as quickly as possible saves lives and is the principle underpinning this guidance."