Studies of the mechanisms and characteristics of ischemic heart disease have increasingly documented evidence of myocardial ischemia in the absence of symptoms. Recent work using objective criteria of ischemic events has confirmed that angina pectoris or its equivalents need not accompany true myocardial ischemia, and this appears to be quite common. The impact of these findings on prognosis awaits further study, but preliminary data suggest an improved prognosis for persons in whom coronary artery disease remains asymptomatic compared with symptomatic patients. Further, reduction of silent ischemic events with nitrate therapy may be associated with a more benign subsequent course. Preliminary trials show a reduction of the number, duration and magnitude of silent ischemic events by transdermal nitroglycerin. Ongoing technical innovations in monitoring systems should allow more complete characterization of this syndrome and lead to definition of medical therapy for it.