An Unexpected Culprit: Nocardia Pericarditis Leading to Cardiac Tamponade in an Immunocompetent Host With Congenital Heart Disease.

We report the case of a woman in her 40s with type II diabetes mellitus and a known ostium secundum atrial septal defect (23 mm, left-to-right shunt) diagnosed one year back. The patient presented with progressive dyspnea on exertion for the last three months, along with low-grade fever and fatigue. Clinical and echocardiographic evaluation revealed massive pericardial effusion with features of cardiac tamponade. Pericardial drainage via a pigtail catheter yielded 650 mL of exudative fluid. Pericardial effusion was negative for fungal culture, malignant cytology, and tubercular workup. Adenosine deaminase was negative, and the effusion was predominantly neutrophilic and exudative in nature. The bacterial culture showed the presence of Nocardia. The patient was started on trimethoprim-sulfamethoxazole, following which there was significant improvement in clinical status over the next month, and the pericardial effusion resolved. This case highlights the importance of early microbiological diagnosis and targeted antimicrobial therapy in patients with pericardial effusion to optimize clinical outcomes, particularly in tuberculosis-endemic countries, where exudative pericardial effusion is often presumed to be of tubercular origin.