Text journal article This exploratory study aimed to analyse physiological interaction processes in equine-assisted-therapy (EAT) between client, therapy horse and therapist.We measured heart rate (HR), heart rate variability (HRV) and cortisol levels before, during and after a standardized therapy session and a control condition in one therapist, four therapy horses and ten female clients in emerging adulthood (Mn = 21.8 years, SD = 3.39). The clients were diagnosed with mild (N = 5) to moderate (N = 5) intellectual disability (ID).There was no significant change in the client's HR, HRV and cortisol levels during an EAT session. No difference was observed between therapy sessions with or without a therapy horse, except during the challenge phase of the EAT protocol, where clients had a significantly lower HR when interacting with the therapy horse. HR between therapist and client correlated significantly, as well as between therapist and horse. This effect was greater when therapists interacted with a familiar horse. Clients' and horses' HRs also correlated, but only when the horse was the clients' familiar and preferred horse.These results indicate that relationship intensity is an important factor for the synchronization process. Moreover, the inclusion of horses in a therapeutic setting can lead to a decreased HR in young adults with intellectual disability while mastering a challenge. Future research should investigate this potential benefit of EAT, considering the reciprocal influences and the relationship between client, therapist and horse. Female Hydrocortisone Analysis Hydrocortisone Metabolism Equine-Assisted Therapy Methods Humans Animals Heart Rate Physiology Horses Saliva Chemistry Young Adult Adult Arousal Physiology Intellectual Disability Therapy Male application/pdf Text Wissenschaftlicher Artikel Testo Articolo di rivista Anna Naber L. Kreuzer Roswitha Zink Eva Millesi Rupert Palme Karin Hediger Lisa Glenk Complementary Therapies in Clinical Practice eng http://creativecommons.org/licenses/by-nc-nd/4.0/ doi:10.1016/j.ctcp.2025.101937 Heart rate and salivary cortisol as indicators of arousal and synchrony in clients, therapy horses and therapist in equine-assisted therapy 2025 Elsevier Copyright © 2025 The Authors open access https://phaidra.vetmeduni.ac.at/o:4082