Two slender nematodes were incidentally found at autopsy in the heart and inferior vena cava of a 36-year-old Japanese man who died of liver cirrhosis. The parasite from the heart measured 29.5 cm by 0.87 mm, and that from the inferior vena cava 26.5 cm by 0.85 mm. The worms were identified as non-gravid adult female Dirofilaria immitis. This is the fourth case of infection with D. immitis in the heart and large vessels.