Partial pericardial agenesis presenting with positional palpitations

Background: Congenital pericardial agenesis is a rare anomaly caused by defective development of the pleuropericardial membrane. Most cases remain clinically silent, but partial defects may predispose to myocardial herniation, coronary compression, or ventricular arrhythmias. Symptomatic presentations are heterogeneous and often non-specific, which contributes to diagnostic delay. Case Presentation: We report the case of a 40-year-old man presenting with intermittent palpitations unrelated to exertion and aggravated by the left lateral decubitus position. Past medical history was unremarkable and patient did not take any chronic medication. Physical examination and laboratory studies, including thyroid function, were innocent. Initial electrocardiography revealed sinus bradycardia with incomplete right bundle branch block and left anterior fascicular block. A 24-hour Holter showed rare polymorphic premature ventricular contractions, and a treadmill stress test was normal. Transthoracic echocardiography demonstrated hypermobility of the apicolateral left ventricular segments and abnormal motion of the right ventricular apex, raising suspicion of pericardial absence. Cardiac magnetic resonance imaging confirmed partial pericardial agenesis involving the apical third of the right ventricular free wall and the apical region of the left ventricle, with reduced systolic excursion and diastolic bulging suggestive of early herniation. No evidence of coronary compression or myocardial ischemia was identified. Given the mild symptom burden and absence of complications, a conservative management plan was adopted. Surveillance consisted of periodic Holter monitoring to assess ventricular ectopy and annual echocardiography to detect potential progression of herniation or development of coronary compression. The patient remains clinically stable with infrequent palpitations and no imaging progression over follow-up. Conclusion: This case illustrates an unusual presentation of partial pericardial agenesis manifesting primarily as positional palpitations. Partial defects may confer a risk of myocardial ischemia or coronary compression and therefore warrant structured long-term monitoring even in minimally symptomatic individuals. Symptom-oriented management, Holter evaluation of ventricular ectopy, and serial imaging are essential to detect evolving herniation or coronary compromise. Increased awareness of this rare entity may facilitate earlier recognition and prevent misdiagnosis.