Electric fans are proposed to mitigate indoor heat stress during heatwaves. Fan cooling threshold temperatures were determined by biophysical models. However, such models could only account for sweating adjustment and disregarded evident cardiovascular impairment in older adults. This study demonstrated the contribution of cardiovascular function adjustment to core temperature responses. Results revealed that focusing just on sweating adjustment greatly underestimated the actual heat stress experienced by older adults. It is not recommended to use biophysical models to determine the threshold temperature of electric fan use for older adults during heatwaves because cardiovascular adjustment was not possible.