A 49-year-old woman with no significant past medical history presented to the emergency room for mild shortness of breath, flulike symptoms of 1 week duration, and myalgia and yellow vaginal discharge of 1 month duration. Moderate pericardial effusion was found upon admission that rapidly worsened into cardiac tamponade. She had a lactic acid dehydrogenase level of 3649 U/L (institutional upper limit of normal = 243 U/L). She was also found to have an exophytic cervical mass, and imaging revealed bulky pelvic disease. Pericardial aspirate as well as biopsy of the cervical mass showed small- to medium-sized cells with scant cytoplasm and open chromatin (panel A) that were CD5 +, CD20 +, CD23 −, and surface λ bright with a high proliferation rate (Ki-67 >95%). In addition, strong cyclin D1 expression was noted (panels B-C).These findings led to a diagnosis of blastoid mantle cell lymphoma in the pericardium and cervix. The patient was in the intensive care unit on pressors and dialysis and was intubated when the diagnosis was made. She was started on definitive therapy with rituximab and hyper-CVAD (cyclophosphamide, vincristine, Adriamycin [doxorubicin], and dexamethasone) and showed dramatic improvement (panels D-E) within the first 5 days of therapy and almost complete resolution of pericardial effusion. The patient was able to leave the intensive care unit and return home.