The aims are to define the exact prevalence of hereditary heart diseases in out-of-hospital cardiac arrest (OHCA) patients taking also into account gender, patient and OHCA characteristics, provincial settings and environmental pollution; to stratify the individualized arrhythmic risk of proband's family members to prevent further sudden cardiac deaths; to refine the classification of the variants of uncertain significance (VUS) on genes which can have the capability to drive to molecular alterations leading to arrhythmogenic hereditary heart diseases. A blood sample will be obtained during resuscitation from all the patients aged ≤50 years suffering an OHCA in Lombardy Region and then analysed for genetic variants possibly causative of cardiac diseases. Genetic data will be merged with patient, OHCA and post-resuscitation data thanks to the connection with LombardiaCARe, whilst pollution data will be retrieved from ARPA Lombardia for free. A genetic counselling and clinical-instrumental evaluation of the proband's first-degree family members will be performed if a pathogenic/likely pathogenic variant or a VUS will be disclosed during the genetic analysis.