Abstract: AIM:To study the effect of heat stress on the expression of reactive oxygen species（ROS）, p22phox and angiotensin II (AngII) in myocardium and to investigate the interrelation among ROS, p22phox and AngII in myocardium. METHODS: Twenty-four Sprague Dawley rats were divided randomly into three groups: control group, high temperature and high humidity stress group and heat stress group. All examinations were performed 4 weeks later. Mean arterial blood pressure (MABP) was measured by carotid artery intubation and ROS was determined with spectrophotometer. Concentration of AngII in plasma and myocardium was detected, respectively, by radioimmunoassay. Expression level of p22phox mRNA in myocardium was determined by reverse transcription polymerase chain reaction (RT-PCR) and p22phox protein was detected by immunohistochemistry and semiquantitative analysis in different groups. RESULTS: Compared with control group, MBP, ROS, p22phox mRNA and p22phox protein levels in high temperature and high humidity stress group and heat stress group significantly increased (P<0.01). No significant difference was observed in LVW/BW index. The concentration of AngII in plasma and myocardium increased markedly. CONCLUSION: The concentration of AngII in plasma and myocardium as well as p22phox in the myocardium increases under heat stress conditions. Heat stress may be associated with overproduction of ROS, possibly by increased expression of AngII.