Introduction and importance: Purulent pericarditis is an uncommon complication of Streptococcus pneumoniae, which commonly occurs in an immunocompromised state such as HIV and can lead to life-threatening complications such as cardiac tamponade and potentially death if untreated. Early identification, pericardiocentesis, and general measures such as antibiotics and anti-inflammatory medications can be life-saving. Case presentation: We present a case of a 64-year-old male with HIV who presented with clinical symptoms suggestive of pericarditis. Chest imaging revealed multifocal airspace diseases and moderate pericardial effusion. He had worsening lactic acidosis, and bedside point-of-care ultrasound showed pericardial effusion with features suggestive of cardiac tamponade. His lactic acidosis improved with emergency pericardiocentesis. Blood and pericardial fluid cultures revealed Streptococcus pneumoniae. He was further treated with intravenous antibiotics, colchicine, and ibuprofen. Clinical discussion: Although Streptococcus pneumoniae is a common etiology of community-acquired pneumonia (CAP), it has not been cited as the leading cause of pericarditis or pericardial effusion. In immunocompromised patients, it is necessary to consider a broad differential diagnosis as an etiology of acute chest pain, as it may be challenging to differentiate pleuritic and pericarditic chest pain from clinical presentation only. Moreover, infectious etiology of acute pericarditis and pericardial effusion should be considered in this patient population, especially those with HIV. At the same time, it is crucial to promptly identify and treat cardiac tamponade to prevent further deterioration. Conclusion: Our case provides insight into the diagnosis and management of CAP and its potential complication of purulent pericarditis and cardiac tamponade in immunocompromised patients.