Right heart failure is a major challenge in clinical practice. Soluble Suppression of Tumorigenicity-2 (sST2), a member of the interleukin-1-receptor family, may have clinical prognostic value. The aim of this study was to analyze whether sST2 correlates with signs of acute right heart decompensation. This prospective single-center study included 50 patients admitted for clinical signs of predominant right heart decompensation. Signs of reduced blood supply to other organs (e.g., renal function parameter, troponin T, NT-proBNP), diuretics, and signs of venous congestion (inferior vena cava (IVC) diameter) with fluid retention (weight gain, peripheral edema) resulting from reduced RV function were analyzed. The degree of peripheral edema was defined as none, mild (5–6 mm depressible, regression in 15–60 s) or severe (>7 mm depressible, regression in 2–3 min). sST2 levels were measured at the day of hospitalization. A total of 78.7% showed severe peripheral edema. The median concentration of sST2 was 35.2 ng/mL (25.–75. percentiles 17.2–46.7). sST2 is correlated with the peripheral edema degree (rSpearman = 0.427, p = 0.004) and the diameter of IVC (r = 0.786, p = 0.036), while NT-proBNP (r = 0.114, p = 0.456), troponin T (r = 0.123, p = 0.430), creatinine-based eGFR (r = −0.207, p = 0.195), or cystatin C-based eGFR (r = −0.032, p = 0.839) did not. sST2, but no other established marker, is correlated with peripheral and central fluid status in patients with decompensated right heart failure.