There are an increasing number of reports of myocarditis associated with mRNA-based COVID-19 vaccination. We describe the case of a female patient with underlying systemic lupus erythematosus, who developed heart failure symptoms following a second dose of the BNT162b2 vaccine. Despite her history of refractory systemic lupus erythematosus, the disease remained stable after she began rituximab treatment. She underwent serial transthoracic echocardiogram and cardiac magnetic resonance imaging for the evaluation of cardiomyopathy. She showed improvement in cardiac function after treatment with glucocorticoids and intravenous immunoglobulin therapy.