Superior vena cava syndrome is a life-threatening condition. Typically, the clinical presentations are gradual; hence, the diagnosis is often delayed until critical compression or obstruction has occurred. Pericardial hematoma is a rare condition that could occur after cardiac surgery. An asymptomatic, 25-year-old female, who underwent surgical atrial septal defect closure 5 days ago, was sent for routine echocardiography examination before discharge. An intrapericardiac hematoma was detected at the right atrium's free wall without any intracardiac hemodynamic consequences. The patient was discharged and planned for monthly evaluation. During follow-up, the intrapericardiac hematoma was expanding. In the third month's follow-up, the patient complained of shortness of breath, headaches, and coughs. Echocardiography evaluation revealed enlarged pericardial hematoma, which compressed the right atrium and superior vena cava orifice, without echo' sign of cardiac tamponade. Computed tomography scan revealed superior vena cava compression by the pericardial hematoma and appearance of the collateral vessel. The patient was diagnosed with superior vena cava syndrome and sent for surgical evacuation. Pericardial hematoma after cardiac surgery should be evaluated meticulously. Chronic expanding hematoma could cause superior vena cava syndrome, which is fatal. Early diagnosis and appropriate treatment are essential in managing this condition.