The trigeminocardiac reflex is a brainstem reflex that manifests as sudden hemodynamic dysfunction including bradycardia, hypotension, hypopnea, and gastric hypermotility due to mechanical stimulation of the trigeminal nerve. Here, the trigeminocardiac reflex was part of the initial patient presentation that led to the diagnosis of maxillary adenocarcinoma. A 54-year-old male presented to the emergency department with a two-month history of right upper jaw pain. Vital signs included blood pressure of 68/48 mmHg, heart rate of 55, and oxygen saturation of 85%. Physical examination showed a swelling on the right side of the hard palate and a right-sided abducens nerve palsy. MRI revealed a 2.8 x 2 x 3 cm enhancing right maxillary mass with retrograde extension along the right trigeminal nerve up to of the midbrain. Transoral biopsy of the mass revealed adenocarcinoma. The bradycardia resolved after successful surgical resection followed by radiotherapy. This case emphasizes the importance of considering brainstem reflexes such as trigeminocardiac reflex in the differential diagnosis of hemodynamic derangements in patients presenting with recurrent sinus symptoms and neurologic deficits.