This study aims to extend the evidence of circulating CILP-1 as a novel biomarker for RVD and prognosis in HFrEF patients by investigating CILP-1 levels in a large cohort of HFrEF on guideline-directed medical therapy (GDMT) and assessing its association with (i) cardiac morphology, function, hemodynamics; and (ii) outcome parameters such as unplanned HF hospitalizations and all-cause mortality. Here, CILP is linked to hydrops fetalis.