Cardiac rehabilitation (CR) reduces mortality and improves quality of life. Unfortunately, participation in CR remains low and studies have examined the use of home-based tele-monitoring to improve participation in CR. These studies generally utilized single- or three-lead electrocardiogram (ECG) channels with limited sensitivity to detect ischaemic changes. In this report, we describe detection of unexpected, significant left main coronary disease in a patient participating in a home CR programme using a unique 12-lead ECG monitoring system.A 68-year-old man was referred for CR after acute coronary syndrome and stent implantation to the obtuse marginal. Three months following this intervention, he began complaining of chest pain. Repeat coronary angiogram showed a borderline lesion in the left main not felt to be clinically significant. The patient performed CR and was monitored with the Master Caution® System, a digital platform including a garment with 10 textile electrodes (Master Caution garment) configuring a device which enables 12 lead ECG. While being monitored, the ECG technician detected 1-2 mm ST-depression in leads 1, L V2-V5. The patient was asymptomatic at the time the ST-depressions were noted. Repeat angiography revealed a significant increase in the severity of the left main lesion and the patient was referred for bypass surgery.This life-threatening diagnosis could easily have been missed using conventional ECG monitoring and our case demonstrates the potential clinical utility of tele-monitoring with a 12-lead digital home ECG monitoring device.