Inclusion Criteria:  Age between 5-18 years old with or without the diagnosis of CHD and symptoms suggestive of rhythm disorders as follows: palpitations and/or syncope and/or dizziness. 24-hours Holter without diagnosis of arrhythmia. Having an smartphone, smartwatch, or tablet (the patient itself or a family member who lives together with the patient) compatible with KMCM. Signed informed consent. In cases under the age of <18 y.o informed consent should be signed by parents or guardians.  Exclusion Criteria:  Concomitant investigation treatments. Being already diagnosed for arrhythmic events. Medical, geographical and social factors that make study participation impractical, and inability to give written informed consent. Patient's refusal to participate in the study.