Vagal reflexes have been well documented in both human and veterinary anaesthetic literature. A trigeminocardiac reflex (TCR) is a vagal reflex frequently documented in human medicine, and subtypes such as the oculocardiac reflex (OCR) are well documented in veterinary medicine throughout numerous species. 1-3 A further TCR subtype, the maxillomandibulocardiac reflex (MCR) has been documented in human literature associated with facial fractures and has recently been described in a sole case report in a dog. 4 Thus far, it has not been documented in a horse. The current case report aims to describe the perianaesthetic management of a horse that developed asystole due to a suspected TCR of either OCR or MCR in origin, in combination with hyperkalaemia of unknown cause which may or may not have contributed to the suspected vagal event, a relationship that has been previously documented. 5,6 Both causes will be discussed as independent or contributory factors.