Although the cause of silent myocardial ischemia (SMI) is unknown, several theories have been advanced to explain the disorder. Most prominent among these are the suggestions that attribute the condition to generalized impaired pain sensitivity and/or enhanced endorphin activity. The present study examined both hypotheses. It was carried out in 33 patients with myocardial ischemia: 13 with silent myocardial ischemia (silents) and 20 with symptomatic ischemia (symptomatics). Pain sensitivity was determined with thermal, electrical, and ischemic pain tests using signal detection theory (SDT) and conventional threshold procedures. To evaluate the significance of endorphin mechanisms naloxone (6 mg i.v.) and placebo were administered on alternate days in a double-blind, cross-over procedure before the pain tests and again before a treadmill exercise test (TET). Somatic pain sensitivity was found not to be impaired in patients with SMI, and no evidence was found to support a causal role for endorphins in the disorder.