Officials of the Chaiyaphum Hospital said Perm Chamnongnok died about an hour before his relatives tried to wake him up from his morning nap at 11:30 am.
He was sleeping beside his house and his relatives wanted to wake him up for lunch when they found he had already died.
Hospital officials said the man had several chronic ailments and the scorching heat of 40 Celsius degree might worsen his condition, leading to heart failure.