Abstract: A heart monitoring device comprises an enclosure with various sensors and components. The enclosure has a first groove on a top surface, sized to fit a phalange of a subject's right hand. When the device is held with the corresponding phalange keyed into the first groove, the device is in a proper orientation for recording the subject's heart activity. The device includes a plurality of electrodes configured to create one or more electrical circuits across a human heart. The electrodes include a right thumb electrode placed on a side of the enclosure for coupling to the subject's right thumb and an upper chest electrode and a lower chest electrode placed on a bottom surface of the enclosure for coupling to the subject's chest. The heart monitoring device also has a plurality of pulse oximeters placed in the first groove and configured to measure blood oxygen levels of the corresponding phalange.