Cardiorenal syndromes (CRS) represent a complex interplay between heart and kidney dysfunction, where impairment in one organ precipitates deterioration in the other. This chapter provides an overview of the types of CRS, including acute and chronic presentations, and highlights the pathophysiological mechanisms that sustain this interplay, such as hemodynamic alterations, neurohormonal activation, and inflammatory responses. We also discuss the roles of natriuretic peptides, inflammatory cytokines, and biomarkers like fibroblast growth factor 23 (FGF23) in disease progression. Furthermore, the chapter emphasizes the importance of understanding humoral signaling pathways to improve diagnosis, prognostication, and treatment of CRS. The goal is to elucidate mechanisms that may help in identifying therapeutic targets to disrupt the pathological cycle between the heart and kidneys, thereby reducing morbidity and mortality.