INTRODUCTION: Congenital pericardial agenesis is a rare congenital anomaly resulting from the incomplete development of the pleuropericardial membranes during embryogenesis, leading to the partial or complete absence of the pericardial sac. Although this condition usually remains asymptomatic, it can present with various misleading symptoms such as chest pain (add some other, maybe 2, more prevalent presenting symptoms), making diagnosis challenging. Advanced imaging techniques are crucial for accurate diagnosis and management, especially when usual diagnostic modalities do not achieve a definite diagnosis. CASE PRESENTATION: The history and diagnostic process of a 16-year-old female who presented with isolated, non-exertional chest pain are detailed. A comprehensive diagnostic work-up was initiated, including chest X-ray (CXR), transthoracic echocardiogram (TTE), CT angiography (CTA), and cardiac magnetic resonance imaging (CMRI). These advanced imaging modalities unveiled the rare and elusive diagnosis of left-sided pericardial agenesis, decisively ruling out other potential causes and shedding light on an extraordinary case that challenges conventional diagnostic pathways. CONCLUSION: Unilateral pericardial agenesis, though typically benign and often shrouded in clinical obscurity, can manifest with enigmatic symptoms such as isolated chest pain, necessitating a meticulous and comprehensive diagnostic approach. Multimodal imaging is essential for accurate diagnosis and for ruling out complications such as cardiac herniation or coronary artery compression. Considering the absence of significant complications, conservative management was chosen in this case, with the patient being discharged with instructions to monitor for any warning signs. CLINICAL KEY MESSAGE: Clinicians should consider congenital pericardial agenesis as one of the potential causes of unexplained chest pain, particularly when the initial investigations are inconclusive. Advanced imaging techniques (such as CXR and MRI) are vital for confirming the diagnosis and subsequently appropriate and timely management and preventing potential complications.