Abstract: At 8:00 a.m. on June 22, 2020, an employee arrived for work, feeling ill. He was assigned to use a string trimmer to clear brush. The crew leader monitored him during the morning and ensured that he drank plenty of water and had access to shade. The temperature was about 84 degrees Fahrenheit, and there was adequate shade available from nearby trees and the carport near the work area. The employee took several breaks during the morning and stated to coworkers and the crew leader that he was able to continue working. After the crew took their lunch break in the shade of the carport, the employee was still feeling ill and had several symptoms such as headache and nausea. The crew leader offered to drive him home or to the hospital, but he refused and left the worksite at approximately 1:00 p.m. driving himself. Upon reaching the city of Napa, approximately 16 miles and about 25 minutes by car, he went to the emergency room at Queen of the Valley Hospital. He was evaluated in the emergency department and admitted to the hospital for four days for cardiac evaluation due to a suspected heart attack. No heat-related illness symptoms were noted in the medical records obtained from Queen of the Valley Hospital. The investigation was referred to the CalOSHA medical unit for evaluation on July 20, 2020. The medical unit returned its opinion on July 22, 2020 and concluded that the illness was not heat-related. CalOSHA identified several causal factors including but not limited to: The employee's symptoms were caused by preexisting health issues and were not associated with the work he was engaged in at the worksite.