OBJECTIVE This investigation compares the frequency of cardiac events during ECG-monitored cardiac rehabilitation in patients who meet the American College of Cardiology (ACC) criteria for monitoring, to the frequency of events in patients in the same program who do not meet the ACC criteria. METHODS Patient charts (n = 289) from a 10-month period were retrospectively reviewed for (1) major and minor cardiovascular events, (2) whether a physician was contacted, and (3) what change, if any, was made in their care plan as a result. RESULTS There were no sudden deaths, fatal or nonfatal myocardial infarctions, or sustained arrhythmias requiring hospitalizations. The overall rate for minor events (angina, nonsustained arrhythmia, ST segment depression) was 26.6%, with no difference noted between men and women. The rate for a new-onset, asymptomatic event was 3.8%. The rate of minor events was greater in patients who met the ACC criteria vs those who did not (p < 0.01), with no detectable difference noted between the two groups regarding the rate of new-onset, asymptomatic events. Four patients (1.4%) experienced a change in their care plan as a result of ECG monitoring. CONCLUSIONS The occurrence of a minor cardiovascular event is common during phase 2 cardiac rehabilitation, and existing criteria satisfactorily distinguish those patients at high risk for experiencing such an event. However, the rate for new-onset, asymptomatic events is rare for both patients classified at high risk and those classified not to be at high risk. Also, only four patients experienced a change in therapy secondary to an event identified by ECG monitoring.