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An 8‐year‐old Leonberger receiving immunosuppressive treatment with clinical signs of acute dyspnea, cyanosis, and difficulty standing was referred to our institution (Day 1). Treatment including oxygen, clopidogrel, and low‐molecular‐weight heparin was initiated for suspected pulmonary thrombosis. However, exertional dyspnea persisted until Day 10, and increased tricuspid regurgitation velocity, pulmonary vascular resistance, and McConnell's signs also were observed. Thus, beraprost sodium was administered PO on Day 11 to treat suspected pulmonary hypertension. On Day 13, contrast‐enhanced computed tomography identified extensive contrast defects in the pulmonary arteries, and IV monteplase was administered on Days 14 and 18, with marked improvement in respiratory status and exertional dyspnea on Day 20. Right ventricular function and McConnell signs also improved, and tricuspid regurgitation velocity and pulmonary vascular resistance decreased. On Day 250, echocardiography indicated further improvement in pulmonary hypertension pathophysiology. The patient was still progressing well with antithrombotic and pulmonary vasodilator treatment 400 days later. [ABSTRACT FROM AUTHOR]

Simple Summary: Pulmonary hypertension is a fatal comorbidity in dogs with left-sided heart disease. Various oral pulmonary vasodilators have been effective in treating canine pulmonary hypertension; however, no studies have compared their hemodynamic effects. This study compared the hemodynamic effects of selected pulmonary vasodilators (15 µg/kg beraprost, 1.0 mg/kg sildenafil, and their combination) in canine models of mitral regurgitation (the most common cardiac disease in dogs). Significant improvements in pulmonary hypertension were observed with all study drugs. Pulmonary vasodilating effects differed among the study's drugs. Sildenafil showed a more potent pulmonary vasodilating effect than beraprost; however, sildenafil significantly worsened the left-heart loading condition. Although beraprost showed a weaker pulmonary vasodilating effect than sildenafil, no significant worsening in the left-heart loading condition was observed. Combination therapy resulted in the strongest pulmonary and systemic vasodilating effects without worsening the left-heart loading condition. This study demonstrated the differences between beraprost and sildenafil in pulmonary and systemic vasodilating effects. Sildenafil involved the risk of worsening the left-heart load, although it was effective in treating pulmonary hypertension. Combination therapy with beraprost and sildenafil synergistically dilated the pulmonary and systemic vessels, indicating a more potent treatment option. Previous reports have shown that various oral pulmonary vasodilators are effective against canine pulmonary hypertension (PH). However, no studies have compared their hemodynamic effects. We aimed to compare the hemodynamic effects of 15 µg/kg beraprost sodium, 1.0 mg/kg sildenafil, and their combination, in dogs with experimentally induced mitral regurgitation. This experimental crossover study evaluated the hemodynamic and functional effects of oral pulmonary vasodilators by application of right-sided heart catheterization and echocardiography. Beraprost significantly decreased pulmonary and systemic vascular resistance. Additionally, beraprost increased right-ventricular stroke volume and left-ventricular cardiac output without worsening left-heart size and left-atrial pressure. The pulmonary vasodilatory effects of sildenafil were stronger, and its systemic vasodilatory effects were weaker than those of beraprost. However, sildenafil significantly increased the left-ventricular volume, left-atrial pressure indicator, and right-ventricular cardiac output. Combination therapy resulted in the strongest pulmonary and systemic vasodilating effects without worsening the left-heart size and left-atrial pressure indicators. Both beraprost and sildenafil were effective against canine PH; however, sildenafil was associated with the risk of worsening left-heart loading. Combination therapy with beraprost and sildenafil synergistically dilated pulmonary and systemic vessels, indicating a more potent treatment option for severe PH cases. [ABSTRACT FROM AUTHOR]