Patients with familial amyloid polyneuropathy (FAP) are now cured by liver transplantation, but cardiac amyloidosis would further progress even after liver transplantation in some patients. To clarify the pathological mechanism of the progress of cardiac amyloidosis in FAP, we investigated cardiac tissues obtained from 6 FAP patients with 3 different types of TTR mutations. One of them had undergone liver transplantation and one year later died of cardiac amyloidosis. We determined clinical severity of cardiac involvement of those patients and characterized amyloid fibril proteins depositing in their cardiac muscles by immunohistochemistry, mass spectrometry and isoelectric focusing. All the patients had cardiac dysfunction and increased cardiac weight. Diffuse deposition of TTR-related amyloid was seen in their myocardium on microscopic examination. Amyloid fibrils of the heart were composed of wild-type TTR as well as variant TTR at a ratio of about 1:1 in 5 patients without liver transplantation. In the patient with a transplanted liver, about 80% of the cardiac amyloid consisted of wild-type TTR. Wild-type TTR contributes greatly to the development of amyloid deposition in the heart of FAP patients regardless of the types of TTR mutations.