Abstract: A mobile cardiac monitoring device is disclosed. The mobile cardiac monitoring device receives voltage-time measurements of a subset of electrocardiogram (ECG) leads for a user, and derives a full set of ECG leads from the voltage-time measurements of the subset of ECG leads. The mobile cardiac monitoring device calculates a heart rate and monitors the cardiac rhythm of the user based on at least one of the subset of ECG leads and calculates a cardiac electrical biomarker (CEB) based on the derived ECG. The mobile cardiac device detects a trigger condition based on the calculated CEB and transmits an alert in response to detecting the trigger condition.