In contrast to studies of the effects of atmospheric temperature and pressure on the occurrence of acute myocardial infarction (AMI), the interaction of these two factors has rarely been studied. We analyzed ambulance data (1993-2002) due to AMI in Hiroshima City using the poisson regression model to examine the main effects and the interaction of atmospheric temperature and pressure on AMI (n=3755). In the analysis, thermohydrological-index (THI), or humidity adjusted temperature, was calculated to involve the effect of relative humidity. The significant influence of atmospheric temperature on AMI was confirmed. Daily events of AMI decreased as temperature increased. Daily events in the low, moderate, and high temperature groups were 1.16, 1.07 and 0.90, respectively (average=1.03/day). Atmospheric pressure showed a weaker effect in the presence of temperature. A more profound interaction was found between temperature and pressure. The highest daily events 1.38 were observed in the low temperature and low pressure group, while this meteorological type was always accompanied by rain and/or snow. It was significant (p=0.047) and 37% higher than that of the high temperature and moderate pressure group. The lowest daily events 0.87 were observed in the high temperature and low pressure group. These associations were reinforced when temperature adjusted by relative humidity was used. Atmospheric temperature and the interaction of temperature and pressure had significant influences on the occurrence of AMI. The highest risk was found on days with low temperature and low pressure. Days with high risk were characterized by winter rain and/or snow.