We describe a case report of a young girl, who presented with symptoms and signs of acute decompensated heart failure not responding to decongestive therapy. Routine 2D echocardiography revealed a diagnosis of constrictive pericarditis. She underwent pericardiectomy, and etiology of it turned out to be CD20 negative B-cell lymphoblastic primary cardiac lymphoma (PCL). Despite intensive medical and surgical management, it was fatal. PCL is uncommon among cardiac tumors and extremely rare in immunocompetent patients. Constrictive pericarditis is a rare clinical diagnosis and manifestation of pericardial involvement in PCL.