The Atrial Natriuretic Peptide (ANP) is a hormone secreted by the heart, and, due to its mechanisms in the central nervous system, it is credited with a possible anxiolytic and stress-reducing effect. The aim of this study consisted of examining the values of ANP in adults and its relationship with anxiety and depression. An exploratory, observational and cross-sectional study was adopted. The sample was composed by 30 attending a Mental Health Service. The Beck Anxiety Inventory and the Beck Depression Inventory were applied, and a negative association between ANP values and the depressive state under Beck scale (p=0.017) was observed, more precisely lower ANP levels in patients with Beck's severe depression state. There were no relevant associations between ANP values and Beck's anxiety states. In order to reinforce this research topic, it is necessary to perform longitudinal studies, gather wider samples and include biological indicators for anxiety and depression as alpha-amylase and cortisol.