This experiment proposed to investigate the efficiency of omega 3 fatty acids from fish that improves autoimmune against myocarditis in the rat. Fish oil was extracted from fresh Tuna fish and performed FAME analysis and mice bioassay. The autoimmune myocarditis was induced by subcutaneous injection of porcine cardiac myosin (PCM) into the footpads of rats on the first and seventh day. Rats were dissected on the 21st day to analyze the histopathological, hemodynamic, echocardiographic factors, and immunohistochemistry expressions. In the study, 73.90% of total fatty acids were recorded. Histological analysis revealed that omega 3 fatty acids administrated groups showed tremendous development in the multifocal myocardia hyaline degeneration and necrosis with inflammatory changes. Moreover, omega 3 fatty acids inhabited the expressions of inflammatory cells (CD4, CD8 and CD11b) and suppressed the level of NF-κB. The echocardiographic factors such as heartbeat, SBP, DBP, levels of LVDs, LVDd, LVPW percentage of LVFS, EF, expression levels of inflammatory cytokines (TNF, IL-1β, IFN-ɤ, IL-2, and IL-6) also significantly suppressed by omega 3 fatty acids. Hence, the present study proved that consuming fatty acid-enriched fish might be a successful therapy for improving the inflammatory profile, regenerates the heart tissues, and controlled the production of inflammatory cells.