The aim of this study was to assess whether serial quantitative assessment of right ventricular (RV) function by speckle-based strain imaging is affected by pulmonary hypertension–specific therapies and whether there is a correlation between serial changes in RV strain and clinical status. RV longitudinal systolic function was assessed using speckle-tracking echocardiography in 50 patients with pulmonary arterial hypertension (PAH) before and after the initiation of therapy. The mean interval to follow-up was 6 ± 2 months. Subsequent survival was assessed over 4 years. Patients demonstrated a mean increase in RV systolic strain from −15 ± 5 before to −20 ± 7% (p = 0.0001) after PAH treatment. Persistence of or progression to a severe reduction in free wall systolic strain (<−12.5%) at 6 months was associated with greater disease severity (100% were in functional class III or IV vs 42%, p = 0.005), greater diuretic use (86% vs 40%, p = 0.02), higher mean pulmonary artery pressure (67 ± 20 vs 46 ± 17 mm Hg, p = 0.006), and poorer survival (4-year mortality 43% vs 23%, p = 0.002). After adjusting for age, functional class, and RV strain at baseline, patients with ≥5% improvement in RV free wall systolic strain had a greater than sevenfold lower mortality risk at 4 years (hazard ratio 0.13, 95% confidence interval 0.03 to 0.50, p = 0.003). In conclusion, serial echocardiographic assessment of RV longitudinal systolic function by quantitative strain imaging independently predicts clinical deterioration and mortality in patients with PAH after the institution of medical therapy.