A laminar color Doppler flow was discovered in the pericardial space in a 35-year-old man with postpericardiotomy effusive constrictive pericarditis. The flow was detected by transesophageal color Doppler echocardiography. A further pulsed Doppler study revealed a to-and-fro flow, which was synchronized with the cardiac rhythm. We hypothesized that this flow was generated by the rhythmic cardiac contraction. It was then augmented by hard fibrous pericardium and became detectable by color Doppler echocardiography. Pericardial effusion is a frequent echocardiographic finding but little attention has been paid to the flow in it. The laminar flow in the pericardial space in our patient is related to his hard pericardium and can aid in making the diagnosis of effusive constrictive pericarditis. We suggest that flow in the pericardial space deserves more attention and may provide valuable diagnostic aid.