An elderly woman died after waiting nearly an hour-and-a-half for an ambulance when she fell over.
Phyllis Asten, 87, was letting out her dog in the garden of her bungalow in Spencer, Northampton, on Tuesday when she fell, her family said.
Her nine-year-old great-grandson Callum Wright was at her house and he raised the alarm with neighbours who called 999 shortly after 4.30pm.
An ambulance arrived just before 6pm and took Mrs Asten, who was conscious, to Northampton General Hospital.
A spokesman for East Midlands Ambulance Service (EMAS) said that as paramedics were waiting to give a clinical handover to Accident and Emergency staff Mrs Asten went into cardiac arrest.
She was taken to the resuscitation area where doctors managed to revive her but she later died.
Michael Diggin, Mrs Asten's son-in-law, arrived at her house not long after her accident and said she broke her hip as she fell on to concrete slabs.
He told the Northampton Chronicle and Echo they were told not to move her but after around 40 minutes decided to bring her in by using a wheelchair because it was so cold.
He told the newspaper: "At the end of the day, I think someone who is taken into hospital by ambulance should be assessed a bit quicker.
"My mother-in-law was very fit and did everything for herself. People do not normally die from broken hips."
EMAS chief executive Phil Milligan said an ambulance was dispatched to Mrs Asten at 4.38pm - she had been categorised by medical staff as needing a 30-minute response - but it had to be diverted to a patient who had suffered a cardiac arrest.
Another ambulance was dispatched when one became free at 5.27pm, he said, and took Mrs Asten to hospital.
He went on: "Whilst waiting to give a clinical handover to A&E staff, our patient went into cardiac arrest.
"The paramedic who was with her at the time shouted for help and took her straight to the hospital resuscitation area, where she was successfully resuscitated.
"We are sorry to hear that she later passed away and offer our sincere condolences to her family and friends."
Northampton General Hospital said an investigation had begun into the standard of care delivered to Mrs Asten.
A spokesman said: "In common with many other hospitals in the local area, Northampton General Hospital's A&E department was under substantial pressure.
"East Midlands Ambulance Service transported 70 patients to the A&E department during the day."
Chief executive Gerry McSorley said: "I offer our condolences to the patient's family. We have now begun a thorough investigation into the care we provided and the circumstances surrounding this patient's death."