Background Previous research has demonstrated accuracies of 70% for the detection of electrocardiogram (ECG) abnormalities by general practitioners. This study aimed to retrospectively assess the level of agreement between GPs and cardiologists of key findings on ECGs. Methods A retrospective study of all patient referrals from GPs sent to a cardiology clinic at a medium sized public hospital over a 3 year period. The ECG diagnosis of the GP and the interpretive function of the ECG was compared with the ECG diagnosis of the cardiologist. Results A total of 2143 referrals were received from 292 GPs from 111 different practices. The level of agreement between the GPs and the cardiologists key findings was 58.9%. In comparison, the level of agreement between the key findings of the interpretive function on the GPs' ECG machines and of the cardiologists was 44.4%. Discussion The GPs' ability to accurately diagnose key findings on the ECG was modest, however, the GPs' ability to appropriately refer based on clinical presentation was exceptional. Based on our findings, the interpretive function on ECG machines should be viewed with extreme caution, particularly when using this to diagnose key findings.