BACKGROUND Asymptomatic postoperative atrial fibrillation (AF) may go undetected. As part of a multicenter observational trial designed to develop a risk prediction score for respiratory depression, the respiratory patterns of patients admitted to standard wards were continuously assessed with capnography and pulse oximetry. The monitor measured end-tidal carbon dioxide, respiratory rate, heart rate (HR), and oxyhemoglobin saturation. CASE REPORT Two men ages 75 and 72 experienced abrupt and variable postoperative changes in HR consistent with AF with rapid ventricular response, coinciding with an abnormal breathing pattern with apneic episodes. In both cases, the changes were not detected by routine clinical monitoring. CONCLUSIONS Continuous capnography identified respiratory distress in 2 patients who experienced symptoms of AF. Continuous monitoring devices can help health care providers minimize the risk of morbidity and mortality for patients at risk of respiratory depression.