We report the case of a 30-year-old man with acute pericarditis in whom effusive-constrictive physiology developed rapidly in less than 2 weeks. Serial echocardiography demonstrated a dramatic change in the appearance of the pericardial effusion and the pericardial space. The patient underwent pericardiectomy with symptom relief. The findings at operation included a markedly thickened and inflamed pericardium. The case highlights the role of echocardiography in the evaluation of patients with pericardial disease and the echocardiographic features that prompted early surgical intervention.