The trigeminocardiac reflex (TCR) is defined as the sudden onset of parasympathetic dysrhythmia, sympathetic hypotension, apnoea or gastric hyper-motility during mechanical/thermal stimulation of any of the sensory branches of the trigeminal nerve. The risk factors that are already known for increasing the prevalence of the TCR include anatomical location, hypercapnia, hypoxemia, light general anaesthesia, age (more pronounced in children), the nature of the provoking stimulus (stimulus strength and duration) and different drugs. Already different potential confounders are also identified. This discussion about risk factors has its importance because of the substantial consequences for functional outcome after intraoperative TCR occurrence. But there remains still a substantial lack of thorough understanding of the TCR, the current treatment options for patients with TCR include a mostly empirical approach: (i) risk factor identification and modification; (ii) prophylactic measures of vital signs and (iii) administration of vagolytic agents or sympathomimetics. In this context, we have now created different thinking models so that we can preoperatively plan a skull base surgery procedure safely in relation to a potential occurrence of the TCR episodes. This chapter provides an overview of this unique reflex that presents a unique interaction between heart and brain. In addition, this also illustrates the mechanism of various cardiac rhythm changes related to the TCR.