A female pug was presented with severe anemia, dyspnea and hemoglobinuria. By B- and M-mode echocardiography, the large number of heartworm were founded in the right ventricle, right atrium and pulmonary artery. The heartworm mass was moved from the right ventricle to the right atrium with the motion of the tricuspid value. Paradoxic septum motion were visible in M-mode of left ventrcular outflow tract and chordae tendineae level short-axis view. Flattened interventricular septum was find in B-mode of papillary muscle level short-axis view. In autopsy, 81 adult heartworms and 7 filarial debris were found. Most of adult heartworm were found in the right ventricle and pulmonary artery. 3 of them were found in the venaca and right atrium, respectively.