Despite the controversy, on October 6, 2021, the World Health Organization (WHO) recognized Long Coronavirus disease (COVID) by officially defining it: symptoms appeared 3 months after the onset of the primary infection by the Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2), persisting for at least 2 months and which cannot be explained by any other condition . Long COVID can affects any type of patient and has polymorphic and fluctuating symptoms over time. The Reunion Island is a French overseas department located in the Indian Ocean accounting more than 860,000 inhabitants. It has recorded since March 11, 2020, nearly 491,825 cases of COVID-19 and 961 deaths of hospitalized patients. Reunion's population is multi-ethnic and younger than the metropolitan France's one. It also has a higher prevalence of obesity and type 2 diabetes, two serious form factors of COVID-19. This specific context makes this island a particular study site for Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) and Long COVID. In addition, some studies have confirmed the involvement of the autonomic nervous system (ANS) in the symptomatology of Long COVID and demonstrated that patients with a Long COVID present a dysfunction of their ANS which is objectified by a reduced Heart Rate Variability (HRV). The regulation of heart rate by the ANS is strongly favored by respiration. A regular slow and deep breathing training helps to adjust the baroreflex, which connect heart rate, breathing and blood pressure. The result of this training is an induced state called cardiac coherence (CC). The investigator therefore hypothesize that respiratory training to CC could re-educate the ANS and durably improve the symptomatology of patients with Long COVID.