We performed continuous echocardiographic examination during the i.v. administration of rtPA in three patients with recent-onset, mobile right atrial thrombosis, in order to assess both the timing and mode of thrombus resolution. In all these cases, right atrial thrombus disappeared before the scheduled dose (100 mg i.v. within three hours) was completed: 60 mg of rtPA were required in the first patient, and 50 mg in the other two. In the first case, the thrombus divided into numerous smaller fragments chaotically moving in the right chambers before disappearing; in the second, the echo reflectivity of the thrombus gradually diminished and the mass showed multiple echo-lucent cavities before disappearing; in last case, the atrial mass migrated from the right atrium to the right ventricle before disappearing. None of the patients experienced any symptoms at the dissolving of the thrombus; bleeding complications occurred in all three (in one, at the site of previous PTCA; in another, at the site of arterial and venous puncture; in the third the haematoma was localized at the site of a previous orthopedic operation) but only two required blood transfusion. In patients with right atrial thrombosis, continuous echocardiographic examination allows us to identify both the timing and mode of thrombus resolution, and the occurrence of new-onset peripheral pulmonary embolization. This information can help in optimizing the dosage of the drug in patients in whom bleeding complications can be suspected to occur after thrombolytic therapy.