A hypercoagulable state has been reported in patients with mitral stenosis (MS) and sinus rhythm (SR). However it has been suggested that the coagulation activity may be increased only within the left atrium in MS, with normal peripheral blood levels. The aim of the present study was to assess regional left atrial and systemic coagulation activities by measuring PF1+2 in patients with severe mitral stenosis and sinus rhythm, normal blood clotting times, and no left atrial thrombus. The study was conducted in 25 consecutive patients with moderate-to-severe MS and sinus rhythm who underwent percutaneous balloon mitral valvuloplasty. Transesophageal echocardiography was performed before the valvuloplasty procedure in all patients to exclude the presence of left atrial thrombus and left atrial spontaneous echo contrast (LASEC). There were no statistically significant differences between LASEC-positive and LASEC-negative patients with respect to age, gender, fibrinogen levels, prothrombin time, mitral valve area, mean mitral gradient, pulmonary artery pressure (in all p > 0.05). Regional (left atrial) PF1+2 levels of both LASEC-positive and LASEC-negative patients were significantly elevated when compared to control subjects (p < 0.01). Statistically significant elevated systemic level of PF1+2 was observed only in LASEC-positive patients when compared to control subjects (p < 0.01, p > 0.05, respectively). In conclusion patients with severe mitral stenosis and SR have increased regional coagulation activity in both LASEC-negative and LASEC-positive groups. Although this increased regional coagulation activity has been reflected in peripheral blood of LASEC-positive patients, it has not been reflected in peripheral blood of LASEC-negative patients.