Background : Recently, it has been shown that pericardial thickness was not increased in certain subset of patients with surgically proven constrictive pericarditis(CP). However, the clinical characteristcs have not been described in detail. Therefore, the purpose of this study was to describe clinical and echocardiographic characteristics of patients with constrictive physiology by comprehensive echo-Doppler study without pericardial thickening in CT or MRI. Methods & Results : From January 2003 to June 2004, eighty-three patients (51 male, mean age 58) were diagnosed as CP by echo-Doppler study. In CT or MRI, the pericardium was of normal thickness in 47 patients (57%; group 1) and was thickened in 36 (43%; group 2). The most common cause of CP in group 1 was previous cardiac surgery (30/47, 65%; mean postoperative period 35 months). However, in group 2, idiopathic was most common (17/36, 49%), and previous cardiac surgery was the etiology of constriction only in 6 patients (17%, p<0.001 vs group 1). Clinical symptoms and physical finding were similar between the groups except peripheral edema and fever were more common in group 2. Atrial fibrillation was more common in group 2 (13% vs 40%, p=0.006). Echocardiographic and radiologic findings were not different significantly except for the presence of pericardial calcification. All patients in group 1 were treated medically and pericardiectomy was performed in 10 patients of group 2 without surgical mortality. During follow-up period (1-10 months, mean 4 months), 4 patients in group 1 and 7 in group 2 showed complete resolution of constrictive physiology with medical treatment. Conclusions : Pericardial thickness was not increased in 57% of patients with constrictive physiology. The etiology was previous cardiac surgery in most patients of this group. The short-term clinical feature was comparable to those with thickened pericardium. However, to investigate the clinical course and prognosis in this group, more long-term follow-up will be needed.