Many new clinical trials about the effect of omega-3 polyunsaturated fatty acids (PUFAs) in heart failure (HF) patients have shown inconsistent results. Therefore, a meta-analysis of randomised controlled trials (RCTs) was performed to determine the benefits of omega-3 PUFAs in HF patients. Articles were obtained from PubMed, EMBASE, and the Cochrane Library. RCTs comparing omega-3 PUFAs with placebo for HF were included. Two reviewers independently extracted the data from the selected publications. The I2 statistic was used to assess heterogeneity. The pooled mean difference and associated 95% confidence intervals were calculated, and a fixed or random-effects model was used for the meta-analysis. A total of nine RCTs involving 800 patients were eligible for inclusion. Compared with patients taking placebo, HF patients who received omega-3 PUFAs experienced decreased brain natriuretic peptide levels and serum norepinephrine levels. Although the left ventricular ejection fraction (LVEF) and clinical outcomes (Tei index, peak oxygen consumption) did not improve, subgroup analysis showed that the LVEF increased in dilated cardiomyopathy (DCM) patients. Overall, omega-3 PUFA supplements might be beneficial in HF patients, especially in DCM patients, but further studies are needed to confirm these benefits.