Abstract: Employee #1, a mason, was laying concrete blocks for the foundation of a retail store. The estimated heat stress reading for the day indicated that heat stress conditions may have existed (WBGT=89 degrees F). Employee #1 was performing continuous moderate work activity for 1 to 2 hours, apparently without taking a break. Because it was Employee #1's first day on the job, he was not acclimated to the heat, and he collapsed and died. A connection between the employee's death and the heat could not be shown. The autopsy report indicated that Employee #1 died of natural causes (heart attack). Apparently, Employee #1 had a history of cardiac dysrhythmia. A 5(a)(1) letter for heat stress was sent to the employer.