Giant cell myocarditis is a rare but often fatal form of myocarditis that often requires cardiac transplantation and has been associated with autoimmune diseases. We describe a 14-year-old female who developed painful proptosis and was diagnosed clinically and histologically with orbital myositis that improved with corticosteroid therapy. Approximately 2 months later, she developed abdominal pain, vomiting, weight gain, and fatigue. She was diagnosed with congestive heart failure and cardiomyopathy, and endomyocardial biopsy revealed giant cell myocarditis. She was treated with immunosuppressive agents and has responded well, without the need for cardiac transplantation. Three previous case reports have described an association between giant cell myocarditis and orbital myositis, but we present the first pediatric case report. We conclude that if orbital myositis is diagnosed in a patient, regardless of age, cardiac function should be closely monitored to detect myocarditis, which may affect the overall outcome.