I thank Drs Arrigo and Huber for their comments on our review in CHEST.1 As Drs Arrigo and Huber point out, comparative epidemiologic studies looking at the prevalence of different World Health Organization groups of pulmonary hypertension (PH) are not available. A community-based, retrospective echocardiographic study2 out of Australia found that the minimum “indicative” prevalence of all groups of PH was 326 in 100,000. In this study, 68% of patients had PH due to left-side heart disease (LHD), and 9% had PH due to respiratory disease or sleep-disordered breathing.2 Patients with PH due to LHD may have been overrepresented in this study, however, as they may be more likely than patients with lung disease to undergo echocardiography. Therefore, we agree with Drs Arrigo and Huber that the prevalence of PH in lung disease may be underestimated. It is also worth noting that many common heart and lung diseases have mutual risk factors, and it may not always be clear whether the cause of PH is one or the other or both.