Background: Since the introduction of gastrointestinal tract endoscopic procedures, there has been concern about cardiovascular complications, especially in patients with coronary heart disease. Although, in general, these procedures are safe, previous studies have documented perturbations in blood pressure, heart rate, and oxygen saturation, as well as the occurrence of arrhythmias and nonspecific ST-segment electrocardiographic changes during such procedures. No studies, however, have specifically addressed the prevalence of silent myocardial ischemia and arrhythmias in patients with well-established coronary heart disease. Methods: During a 15-month period, 25 hospitalized patients with well-defined coronary heart disease underwent continuous ambulatory electrocardiographic recording during endoscopic procedures requiring intravenous sedation, as well as during a prolonged baseline period. All patients were considered clinically stable, although 92% were categorized as being at intermediate or high coronary risk by standard risk stratification criteria. Eleven patients (44%) had had previous myocardial infarction, and 68% reported a history of angina. Results: Although 24% of patients had one or more episodes of electrocardiographic ischemia during the recording periods, no patient had evidence of ischemia exclusively during the endoscopic procedure. Arrhythmias were no more frequent during the endoscopic procedures than during a corresponding baseline period. Symptomatic angina or serious arrhythmias did not occur during the procedures. Conclusions: Our data suggest that endoscopic procedures in patients with stable but severe coronary heart disease, when performed with standard medications, monitoring, and techniques, rarely result in silent or symptomatic myocardial ischemia or serious arrhythmias. In addition, although asymptomatic minor arrhythmias are common during endoscopic procedures, their occurrence appears less frequent than during daily hospital life. © 1993, American Medical Association. All rights reserved.