Introduction: Influenza viral infections are typically self-limiting; however, they have been recognized as an important cause of viral myocarditis. Among the influenza subtypes, Influenza A has been most frequently associated with myocarditis in reported medical literature. In contrast, myocarditis secondary to Influenza B infection is rare, with even fewer cases documented in the pediatric population. Case presentation: We report an eight-year-old girl who presented with features of cardiogenic shock including hypotension, tachycardia, and low urine output, with a prior history of febrile lower respiratory symptoms for three days and a household contact of similar illness. 2D echocardiography revealed moderate LVH with LV systolic dysfunction (EF-54%) and a thinrim of pericardial effusion. Troponin I elevated (1185 ng/mL) with ECG showing nonspecific STsegment changes consistent with myocarditis. Inflammatory markers elevated along with deranged liver functions, suggesting a viral etiology . Respiratory viral panel demonstrated positive Influenza B virus PCR from a throat swab, while testing for CMV , EBV , parvovirus, SARSCoV- 2, and Mycoplasma pneumoniae returned negative results. The child received supportive cardiac care including meticulous fluid management, inotropic support, and antiviral therapy with oseltamivir in the intensive care unit. She gradually improvedwith anti-inflammatory therapy using IV methylprednisolone and anti-heart-failure regimen, continued for six weeks. Conclusion: Influenza B fulminant myocarditis is a rare but life-threatening clinical condition in children. It may progress rapidly to heart failure, carries a high risk of poor prognosis, and requires intensive treatment. This case highlights the importance of seasonal influenza vaccination in children to reduce both typical and atypical complications.