Docosahexaenoic acid (DHA) is an omega-3 fatty acid found primarily in fish oil and algae. Its use in supporting or treating congestive heart failure (CHF) is based on its broader cardiovascular benefits, particularly its anti-inflammatory, anti-arrhythmic, and lipid-modulating properties. Several clinical studies and meta-analyses have evaluated the effects of omega-3 fatty acids (including DHA and EPA) in heart failure patients. Some evidence suggests that supplementation can improve cardiac function, reduce inflammatory markers, and possibly decrease hospitalization rates in CHF patients.

The best-known trial, GISSI-HF (2008), found that supplementation with omega-3 fatty acids, including DHA, led to a modest but statistically significant reduction in all-cause mortality and hospitalizations for cardiovascular reasons in patients with heart failure. However, the benefits were relatively small, and later studies have produced mixed results, sometimes failing to show a significant effect. Most major guidelines acknowledge omega-3 fatty acids as a possible adjunctive therapy in heart failure, but typically with a weak recommendation due to the modest size of the effect.

While DHA is not a primary or standalone treatment for CHF, there is enough scientific evidence to justify its adjunctive use in some patients. The overall evidence supporting DHA specifically (as opposed to combined omega-3s) is limited, and the rating reflects the modest and sometimes inconsistent findings.