Purpose: To report the risk of fatal atrial migration with the Tempofilter. Methods: Among temporary filters, the high safety profile Tempofilter has been marketed as offering protection for up to 6 weeks. We implanted about 60 Tempofilters to prevent pulmonary embolism. The main indications were temporary thromboembolic risk, recurrent pulmonary embolism, and contraindication to or failure of anticoagulant therapy. Follow-up was performed regularly by plain abdominal film and Doppler ultrasound. Filters were removed about 4 weeks after placement. Results: We encountered three cases (5%) of atrial migration and one case of 5-cm cephalad displacement of the filter. Of the three patients with atrial migration, two died within 3 days of implantation, one from a massive pulmonary embolism and the other with cardiac tamponade. One patient did not show any serious complications. Conclusions: The Tempofilter may actively migrate cranially and become dangerous in the case of migration within the heart.