We compared the diagnostic accuracy of 3-lead tele-ECGs to both 12-lead tele-ECGs and a conventional 12-lead ECG device (the gold standard). The subjects were older people (n = 107) with a mean age of 66 years. The overall agreement between two cardiologists on interpreting the 3-lead tele-ECG recordings was 97% (kappa = 0.96, P < 0.001) and it was 91% for the 12-lead tele-ECGs (kappa = 0.90, P < 0.001). We also found excellent agreement on the interpretation of the 3-lead tele-ECGs compared to the gold standard: 98% (kappa = 0.96, P < 0.001) and for the 12-lead tele-ECG compared to the gold standard: 98% (kappa = 0.96, P < 0.001). Bland-Altman plots showed that the apparent differences between the techniques were not clinically relevant. The use of a 3-lead tele-ECG device may be useful for reducing the delay in treating specific heart disease conditions, e.g. in older people affected by chronic heart disease who need frequent ECG monitoring.