An electrocardiogram (ECG) sensor has a flexible thin ring-shaped substrate configured to be worn about a patient's finger. The substrate has an inner surface and an outer surface opposite the inner surface. A first ECG electrode is positioned at the outer surface of said substrate and a second ECG electrode is positioned at the inner (or outer) surface of the said substrate in contact with the finger (or the adjacent finger if the electrode is on the outer surface), whereby the two ECG electrodes receives a single-lead ECG signal when the first electrode is touched to the patient's body. Touching different locations on the body or wearing multiple rings can provide multi-lead ECG measurements. The ring shape can be converted to a wearable patch for continuous ECG measurements.
