Laminar flow within large vessels or organs can cause artifact that may simulate thrombus during computed tomographic study. The degree of venous enhancement depends on the size of blood pool and cardiac output in relation to the time of scanning. When venous structures are scanned too fast after injection of contrast material, poor mixing of enhanced and unenhanced blood creates flow artifact that gives an appearance of deep venous thrombosis. As compared with dynamic computed tomography (CT), because of a shorter acquisition time of spiral CT, vascular and organ enhancement on spiral CT scan are more dependent on factor that affect delivery of contrast material into the blood stream. Differentiation from true thrombus can be made by use of delayed scan as well as increased density and finding of relatively poor margination of artifact. In addition, both angiography and echocardiography could complement CT to assure that false-positive results are minimized. We experienced a case of artifact mistaken for intracardiac mass on spiral CT, but it was not noted on echocardiography.