This is a comprehensive tutorial reference to the science, diagnosis and possible treatment of trigeminal cardiac reflex (TCR) initiated when the trigeminal nerve is disturbed usually during intercranial surgery. The trigeminal nerve is the largest of the cranial nerves, and provides sensory supply to the face, scalp, and mucosa of the nose and mouth. TCR is defined as the sudden onset of parasympathetic dysrhythmia, sympathetic hypotension, apnea, gastric hyper-motility during stimulation of any of the sensory branches of the trigeminal nerve. The related oculocardiac reflex (OCR), first isolated in the early 20th century was encountered during eye surgery where the trigeminal nerve outside the skull was disturbed. Since first reported in 1999 by Co-Editor, Bernhard Schaller, research focused on TCR is expanding and while the instance is rare, as more is discovered about TCR increased diagnosis and more effective treatment protocols will evolve. This book will be of interest to clinical and research neurologists as a general introduction for clinical presentation and as a foundation for research.