Intra-cardiac thrombi include both left- and right-sided thrombi (RST). While left-sided thrombi, such as those in the left atrial appendage and the left ventricle, are not uncommon, RSTs are exceedingly rare yet carry a high mortality. The broad categories of RST include true thrombi and tumor thrombi. This chapter discusses the etiology, diagnosis, echocardiographic appearance, and clinical implications of right-sided thrombi.