Background Endoscopy is useful for diagnosis and treatment of upper gastrointestinal bleeding (UGIB). However, both endoscopy and UGIB may compromise the cardiovascular function. The present study is to investigate the cardiovascular responses of emergency endoscopy for patients with UGIB and stable coronary artery disease (CAD). Methods Consecutive 50 patients with known CAD and 50 patients without CAD history (non-CAD group) in whom emergency endoscopy was requested for UGIB were prospectively enrolled. All patients received ambulatory electrocardiographic monitoring before, during, and after endoscopies. Cardiac indices including supraventricular and ventricular arrhythmia, ST ischemic change, and autonomic nervous function evaluated by heart rate variability were compared. Results All patients in both groups had successful primary hemostasis, and peptic ulcer bleeding was the main etiology (82%). Compared with the non-CAD group, patients with CAD had a significantly higher incidence (42% vs 16%, P = .004) and frequency (1.19 vs 0.12 events per minute, P = .003) of ventricular arrhythmias during endoscopy. Nine patients with CAD and 1 patient without CAD had ischemic ST changes ( P = .016). Comorbidity with congestive heart failure was not only associated with a higher frequency ( P = .02) but also a more severe fluctuation ( P = .002) of ventricular arrhythmia. None in both groups had angina or MI before, during, or after endoscopy. Heart rate variability did not show a difference. Conclusions Ventricular arrhythmias and myocardial ischemia, although mostly subclinical, were common in patients with stable CAD undergoing emergent endoscopy for UGIB, especially in those with concomitant congestive heart failure.