A Texas postman died on his round as the heatwave sweeping the region showed no sign of abating.
Eugene Gates Jr, 66, collapsed in the front yard of a home in Dallas. The property owner rushed out to try to revive him, but to no avail.
While the US Postal Service has not confirmed whether Mr Gates died from the heat, the temperature in Dallas reached 46.1C (115F), the highest in the city since 1980, on Friday. Other cities in Texas also recorded their hottest days on record.
According to the National Weather Service, the heat reached a level likely to cause cramps and exhaustion, especially for those without air conditioning.
It is estimated that more than 270 delivery drivers working for the US Postal Service (USPS) and major delivery company, UPS, have suffered serious heat exposure since 2015.
According to a joint investigation by Columbia Journalism Investigations, National Public Radio and The Texas Newsroom it is estimated that at least 53 Texas workers have died as a result of extreme heat since 2010.
However Greg Abbott, the governor of Texas, has just signed an ordinance which would end mandatory heatwave water breaks demanded in several cities including Dallas and Austin.
The heatwave, which has already lasted a week, is expected to continue into early July and spread to Oklahoma, Kansas and Arkansas.
It is feared that the longer the heatwave lasts, the greater the risk to human life.
"Not only are the daytime temperatures and dew points abnormally high, producing some record heat index readings, but the overnight lows are also close to or at record levels," Alex Lamers, a forecaster with the Weather Prediction Centre told the New York Times.
The heatwave has also threatened the power grid, with officials in Texas pleading with residents to conserve energy.
On Friday morning, there were more than 100,000 homes and businesses without power in Texas, Louisiana and Oklahoma.
Responding to Mr Gates's death, the USPS said: "The postal service is deeply saddened by the loss of life. our thoughts are with his family, friends and colleagues at this time."
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