We experienced a case of T-cell lymphoma demonstrating diastolic heart failure as an initial manifestation. An 81-year-old Japanese male was admitted to the University of Tokyo Hospital because of progressive dyspnea and general fatigue. Clinical presentation was congestive heart failure and cervical lymphadenopathy. Right heart catheterization revealed "dip and plateau" waveforms in right ventricular pressure, which suggested a constrictive nature of heart failure. Gallium scintigram showed marked uptake in the heart. Biopsy from a cervical lymph node confirmed the diagnosis of malignant lymphoma of T-cell origin. Diastolic heart failure remained after successful chemotherapy. Autopsy revealed pericarditis with severe adhesion of the pericardium and the epicardium.