The man, said to have been suffering from a chronic ailment, was found at Ciudad Real in the centre of the country. His body had registered a temperature of 40 degrees Celsius (104 degrees Fahrenheit) at the time of its discovery.
Health Minister Elena Salgado said six peoeple had been hospitalised in Andalusia due to the effects of heat.
Meanwhile electricity consumption in Spain has soared to new summer records due to increased use of air conditioning and refrigerators, the utility operators Red Electrica de Espana (REE), announced.
By Wednesday consumption had reached a peak of 36,800 megawatts, overtaking a Tuesday record of 36,700 megawatts, they said.
A power supply breakdown in Seville Tuesday temporarily deprived tens of thousands of the use of electric fans and air conditioning.
In Seville province, where temperatures have reached 40 degrees Celsius during the past few days, authorities have ordered a red alert, the highest level of a heatwave emergency scheme introduced in May by the new Spanish Socialist government.
In Madrid Tuesday, temperatures soared to a 73-year high of 39.3 degrees centigrade, according to the national meteorological institute.
Temperatures topped 40 degrees Celsius in seven provincial capitals -- Cordoba, Badajoz, Seville, Caceres, Toledo, Granada and Ciudad Real. The highest recorded temperature -- 42.3 degrees centigrade (108.1 degrees Fahrenheit) was in Cordoba.
A heatwave killed at least 141 people in Spain last year.