The initial assumption that sudden acute chest pain may be of cardiac origin is justifiable, but when this proves not to be the case the patient is left with little explanation of the cause. It is suggested here that diaphragmatic cramp may be a cause of some undiagnosed noncardiac chest pains associated with mandibular referred pain. The phrenic nerve provides both motor and sensory innervation to the diaphragm, while the trigeminal nerve carries sensation from the mandibular teeth. Both nerves originate in separate nuclei close together in the lower medulla. Interconnections between these nuclei and others higher up in the brain may provide one explanation for this problem.