The French health minister, Jean-Francois Mattei, who commissioned the probe into 11,435 more deaths than usual, escaped censure in its report, released on Monday.
However, the senior civil servant in charge of the national health service has resigned over his handling of what the report described as a “catastrophe”.
Health services also struggled to cope with August's deadly heatwave because of understaffing due to medical staff taking holiday, the three doctors who conducted the inquiry said.
"For want of anticipation, organisation and coordination, the response was not appropriate," said the report.
The mostly elderly victims died during the first two weeks of August, when temperatures soared above 40C (104F) in the worst heatwave since records began in 1945, causing dehydration and hyperthermia.
"The catastrophe arose while there were no measures in place to cope with the heat," the doctors' report added.
Health Minister Jean-Francois Mattei does the rounds
The report deals a blow to the prestige of a health service vaunted as the world's best, but which was overrun by heat-stricken patients. The rise in deaths has led the government to consider scrapping a public holiday to fund extra care for the elderly.
The report suggested improving the organisation of hospital emergency services and looking into installing air conditioning, which most French hospitals do not have.
Eight days late
Poor communication between the health ministry, other government departments and medical services on the ground meant all involved failed to grasp the scale of the problem early on.
"The pooling of available information ... would have allowed the exceptional nature of the phenomenon to be detected earlier ... such that action could have been taken faster, in a more coordinated way and more effectively," the report said.
France's opposition socialists have accused Mattei of acting too slowly. He put the health service on an emergency footing and recalled holidaying medical staff on 14 August, but official figures show the death rate began rising on 6 August.