The system and method defined herein are intended to detect, monitor and characterize in a non-invasive way cardiac arrhythmias of a patient that are associated with the development of atrial arrhythmia and increased risk of ischemic cerebral stroke. The system consists of a portable device with integrated sensors for biosignals; integrated modules in the portable device for recognition of intermittent atrial arrhythmia episodes; a module for characterization of the distribution of atrial arrhythmia episodes aiming to assess disease progression. The proposed is a technical solution allows for long-term monitoring of atrial fibrillation in a non-invasive way for the patient. If a non-documented atrial arrhythmia is detected by automatic means during the long-term monitoring, a physician is informed by e-mail by sending the electrocardiogram of the said arrhythmia episode. If the physician confirms diagnosis of atrial fibrillation, a recommendation for immediate medical attention is sent to patient's smart device.