BACKGROUND Although diffuse large B-cell lymphoma (DLBCL) is the most common subtype of non-Hodgkin lymphoma in adults, isolated cardiac recurrence of DLBCL which can cause fatal heart failure via various mechanisms is extremely rare. Furthermore, the frequency of recurrence of DLBCL more than 5 years after attaining complete remission is as low as 3.6%. The rate of complete remission and partial remission of DLBCL that have recurred 5 or more years after attaining the initial remission are reported to be 61% and 29%, respectively. CASE REPORT A 79-year-old female with a history of DLBCL at the age of 63 years was transferred to our hospital because of cardiogenic shock. Although cardiac tamponade was suspected, her hemodynamics did not improve with pericardiocentesis. Thoracotomy showed an elastic to hard tumor occupying most of the right ventricular wall. Cytological examination of the pericardial effusion and histological examination of a biopsy of the tumor yielded a diagnosis of DLBCL; this information was available only post mortem. Immunostaining of a biopsy specimen suggested that her cardiac tumor was a recurrence of her lymphoma diagnosed 16 years previously. Bone marrow aspiration was not performed; no recurrences were detected in any other site. This patient thus appeared to have an isolated cardiac recurrence of DLBCL. CONCLUSIONS When managing a patient with a cardiac tumor and a past history of DLBCL, albeit more than a decade previously, establishing a histological diagnosis as early as possible would facilitate possible successful treatment and a good prognosis.