HSF1 and Infertility: Previous findings have shown that single Hsf1‐null male mice exhibit morphological abnormalities in their sperm heads but are fertile.[27] Single Hsf2‐null male mice also exhibit a small impairment in male fertility and still produce offspring.[28, 29] Interestingly, simultaneous deficiency of both Hsf1 and Hsf2 results in the complete absence of sperm and spermatocyte arrest at the pachytene stage, resulting in complete infertility.[29] Therefore, it is speculated that HSF1 and HSF2 might have a compensatory relationship.