We report the cases of two patients admitted to the Emergency Department with a clinical picture of right heart failure. An emergency echocardiograph suggested an intra-cardiac tumor which turned out to be a primary intra-cardiac lymphoma in one case, and a diffuse lymphoma principally localised in the heart in the other. Echocardiographic, CT and MRI investigations clarified the sites, as well as anatomical relations and extensions. Histology confirmed the diagnosis, and allowed classification of the lymphoma in order to decide on treatment. A PET scan performed in one patient illustrated the response to treatment. The respective significance of each of these investigations is discussed, in addition to the management. While transthoracic echocardiography remains the key element in the acute management, MRI and PET scans are being used more and more often for determining the character of these lesions, as well as for assisting with therapeutic decisions and for follow-up.