Right ventricular enlargement in heartworm disease.

The size of the right ventricle of 15 dogs with spontaneous Dirofilaris immitis microfilaria was evaluated by thoracic radiography, electrocardiography, and right ventricular free wall weights. Based on electrocardiography and right ventricular weights, none of the 15 dogs had evidence of right ventricular hypertrophy. Based on radiography, only 2 of the 15 dogs had right ventricles of normal size. Right ventricular dilation in the absence of right ventricular hypertrophy was demonstrated. The right ventricle appears to dilate, prior to hypertrophy, in response to D immitis infestation.