Trigeminocardiac reflex (TCR) is a reflexive response of bradycardia, hypotension and gastric hypermotility which is observed upon mechanical stimulation in the distribution of the trigeminal nerve. Previous articles have described TCR during intracranial operations, ophthalmic surgery, microcompression of the trigeminal ganglion and radiofrequency lesioning of the trigeminal ganglion. TCR may occur during transarterial embolization of dural arteriovenous fistula (DAVF) with Onyx, leading to a significant decrease in heart rate under a standard anesthetic protocol. TCR may also occur due to chemical stimulus of dimethyl sulfoxide (DMSO) in transvenous Onyx embolization of dural cavernous sinus fistula. Slow rate of injection may give DMSO enough time to dissipate in the blood stream which is important for the prevention of toxicity. This report confirms that the reflex was blunted by the anticholinergic effects of atropine and there was no harm to patients if stopped immediately.