Mild radiographic lesions of canine heartworm disease in a 5-year-old German Shepherd, lateral projection. Although nearly normal, the apical pulmonary artery appears to be slightly larger than its corresponding vein, suggesting developing pulmonary hypertension. Ao, aorta; CVC , caudal vena cava; PA, pulmonary artery; PV, pulmonary vein; RA, right atrium; LA, left atrium; RV, right ventricle; LV, left ventricle.