Right atrial thrombi have been diagnosed more frequently since the widespread use of two-dimensional echocardiography. The authors present current opinions on etiology of right heart thrombi. They can originate from two sources: type A thrombi originate in deep peripheral veins; they have worm-shape and they are extremely mobile or they develop within the right heart chambers-type B-they are then parietal and immobile. Clinical significance, prognosis in both types of thrombi is discussed and the guidelines for treatment are presented. Type A patients are a high risk group because of frequent incidence of severe pulmonary embolism and excessive mortality rate so aggressive therapy is required (surgery or fibrinolysis when surgery is contraindicated). Type B thrombi are much more benign, usually they do not lead to the death and treatment with anticoagulants seems to be sufficient.