Pericardial effusion (PE) is a common finding in cardiac patients with chronic heart failure. The prognostic relevance of a small, haemodynamically non-compromising PE in such patients, however, remains to be determined. All patients referred to our heart failure clinic and having a baseline echocardiography and follow-up clinical visits were included. Patients with a haemodynamically relevant PE, acute myo-/pericarditis, systemic sclerosis, rheumatoid arthritis, heart transplantation, heart surgery within the last 6 months or malignancies within the last 3 years were excluded. Patients with or without a haemodynamically irrelevant PE were compared regarding all-cause mortality as the primary and cardiovascular death or need for heart transplantation as secondary outcomes. A total of 897 patients (824 patients in the control vs. 73 patients in the PE group) were included. In the PE group, left ventricular ejection fraction (LVEF) was lower [31, interquartile range (IQR): 18.045.0] than in controls (34, IQR: 25.047.0; P 0.04), while the end-systolic diameters of the left ventricle and the left atrium were larger (P 0.01 and P 0.001, respectively). Similarly, in patients with PE, the right ventricle (RV) systolic function was lower (P 0.005 for both the fractional area change and the tricuspid annulus movement), the dimensions of RV and right atrium (RA) were larger (P 0.05 for RV and P 0.01 for RA), and the degree of tricuspid regurgitation was higher (P 0.0001). Furthermore, in the PE group, the heart rate was higher (P 0.001) and the leukocyte count as well as CRP values were increased (P 0.004 and P 0.0001, respectively); beta-blocker use was less frequent (P 0.04), while spironolactone use was more frequent (P 0.03). The overall survival was reduced in the PE group compared with controls (P 0.02). Patients with PE were more likely to suffer cardiovascular death (1-year estimated event-free survival: 86 5 vs. 95 1; P 0.01) and to require heart transplantation (1-year estimated event-free survival: 88 4 vs. 95 1; P 0.009). A multivariate Cox proportional hazard model revealed the following independent predictors of mortality: (a) PE (P 0.04, hazard ratio (HR): 1.95, 95 confidence interval (CI): 1.03.7), (b) age (P 0.04, HR: 1.02, 95 CI: 1.01.04) and (c) LVEF 35 (P 0.03, HR: 1.7, 95 CI: 1.12.8). In chronic heart failure, even minor PEs are associated with an increased risk of all-cause mortality, cardiac death, and need for transplantation.