Purulent pericarditis is uncommon among paediatric patients and cases caused by group A Streptococcus (GAS) are even rarer. We report a four-month-old female infant who was referred to the Royal Hospital, Muscat, Oman, in 2015 with pericardial effusion and cardiac tamponade. She had initially presented to a secondary hospital with a two-week history of fever, a runny nose and shortness of breath. Blood and pericardial fluid cultures confirmed GAS isolates. The infant was treated with a two-week course of antibiotics and made a complete recovery with no echocardiographical evidence of pericardial effusion at a two-month follow-up. To the best of the authors' knowledge, this case constitutes the youngest infant to present with GAS pericarditis. As invasive GAS infections can present in infancy, early recognition and treatment is required.