Some patients with group 3 pulmonary hypertension (PH) (PH due to lung disease and/or hypoxia) exhibit disproportionately advanced or "out-of-proportion" PH. In the present case series, we document four consecutive patients with progressive out-of-proportion group 3 PH. All patients exhibited progressive dyspnea or peripheral edema and were treated by pulmonary artery hypertension (PAH)-specific vasodilator(s). At the follow-up assessment 3-4 months later, symptoms/signs and pulmonary hemodynamic measurements improved in all four patients (45 ± 8% decrease in pulmonary vascular resistance). Pulmonary oxygenation deteriorated in one patient but improved or did not significantly change in the remaining three cases. Importantly, the background lung parenchymal disease (early-onset chronic obstructive pulmonary disease, rheumatoid arthritis-associated interstitial pneumonia, and combined pulmonary fibrosis and emphysema) was stable upon progression of the right heart failure symptoms/signs, and also during the 3-4-month follow-up period in all cases. We herein describe the clinical features of the four cases and discuss the potential benefits and risks of PAH-specific treatment in this emerging population.