Ischemia/reperfusion (I/R) caused by cardiac arrest (CA) and subsequent cardiopulmonary resuscitation (CPR) was the primary cause of post-cardiac arrest syndrome (PCAS), including post-cardiac arrest myocardial dysfunction and post-cardiac arrest brain injury. Disturbance of endoplasmic reticulum proteostasis, so-called endoplasmic reticulum stress (ERS) was one of the pathological changes induced by I/R injury. The unfolded protein response (UPR) was an adaptive response triggered by ERS in cells. Modulating the UPR arms to alleviate ERS to promote cell survival was promising for attenuating I/R injury. Activating the activating transcription factor6 (ATF6) signaling pathway, one of the arms of the UPR, confers protection against I/R injury in multiple tissues by restoring endoplasmic reticulum proteostasis and reducing oxygen free radicals. This article reviewed the structural characteristics and biological function of ATF6 and focused on its essential role in cardiac and cerebral I/R injury as well as potential therapeutic targets, hoping to provide new ideas for the effective treatment of PCAS.