In today's VETgirl online veterinary continuing education podcast, we review pulmonary hypertension (often called cor pulmonale) and the use of sildenafil (more famously known as Viagra). Pulmonary hypertension is classified is as an increase in either pre-capillary (pulmonary arterial ) or post-capillary (pulmonary venous) pulmonary resistance. In dogs, the disease occurs most commonly in older, small breed dogs as a result of chronic lung disease, chronic left-sided heart disease, heartworm infection, pulmonary thromboembolism, or left-to-right cardiac shunts (which is one of the reasons why it's so important that you treat underlying lung disease before it progresses to pulmonary hypertension!). The clinical signs of pulmonary hypertension may be indistinguishable from primary respiratory disease or congestive heart failure and includ tachypnea, cyanosis, dyspnea, increased respiratory effort, syncope, etc. Definitive diagnosis of pulmonary hypertension is made via echocardiogram by estimation of pulmonary artery pressures (typically, a dog needs to have tricuspid regurgitation to have this measured on echo). Thoracic radiographs remain an important component to the medical workup in these patients (usually performed prior to echocardiography).