Poor communication and the absence of doctors on August leave were among the factors behind France's heatwave tragedy, an official report has found.
Thousands died across Europe
The 35-hour week also contributed, says the inquiry, set up to examine why more than 11,400 people died.
The report describes what happened as a "health catastrophe".
It found that health authorities were not fully aware of the unfolding crisis on the ground.
Many of the dead were elderly people, unable to cope as temperatures soared to 40C (104F).
The inquiry was set up by Health Minister Jean-Francois Mattei after the government was criticised for its slow response to the crisis.
France - 11,400
Netherlands - 1,400
Portugal - 1,300
UK - 900
Spain - 100
Information on the scale of the crisis was not pooled because the health ministry, other government departments and workers on the ground were so compartmentalised, the report says.
The August leave system - which also meant the cabinet was absent as the crisis took hold - comes in for strong criticism.
The mass departure of doctors on holiday had a severe impact on the working of the emergency system, it says.
It suggests better organisation of the healthcare system, liaison between weather services, hospitals and those caring for the elderly, and better provision of beds for elderly patients.
Lorries were used as overflow mortuaries
"An adequate alert, watch and information system would have allowed those involved to act more quickly in implementing measures to adapt the health care system, " said the report.
France's surgeon-general resigned last month after ministers publicly blamed his department for failing to alert them to the crisis.
On Monday, officials in the Netherlands said as many as 1,400 Dutch people died in the heatwave between June and August.
The total is up on an earlier Dutch official estimate that between 500 and 1,000 people died.
In August - the peak of the extreme heat - temperatures repeatedly topped 30C, in a country where the average would normally have been 22C (72F).