A method and wearable device for diagnosing personal cardiac health condition by monitoring and analyzing heartbeat includes a motion sensor detecting whether the user is in a motion state a heart rhythm sensor detecting the users signal of heartbeat interval a memory storing algouthm program and database for data process, comparison, and analysis a microprocessor calculating, filtering and judging the signal of heartbeat interval and a feedback module displaying or alarming a judgment result, wherein the wearable device continuously detects the users motion state and heartbeat condition, and detects heart rhythm when the user is not in the motion state to further judge the users cardiac health condition, such as atrial fibrillation. The method comprises the steps of detecting a heartbeat signal when the user is judged not to be in motion, judging whether there is atrial fibrillation or another type of arrhythmia based on heartbeat intervals.
