Inhaled iloprost is an effective therapy for patients with pulmonary arterial hypertension (PAH); however, some patients experience extended inhalation times when using the V10 formulation (10.0 µg/mL) to deliver a 5 -µg dose (at mouthpiece) and are at risk of incomplete inhalations and reduced inhalation frequency. VENTASWITCH was an observational, case-crossover study to evaluate inhalation behavior in patients with PAH switched from iloprost V10 to V20 (20.0 µg/mL) formulation for delivering a 5 -µg dose using the I-Neb® AAD® device. Adults with PAH participating in a German Ventavis® (iloprost) patient-support program, who were switched from the V10 to V20 formulation, were enrolled. The co-primary endpoints were mean daily proportion of complete inhalations and mean daily inhalation frequency. The secondary endpoint was mean daily inhalation duration. Data were collected for three months before and after switching. Overall, 63 patients were included. Switching from V10 to V20 resulted in a significant increase in the mean daily proportion of complete inhalations (92% vs. 97%, P < 0.0001) and inhalation frequency (4.6 vs. 4.9 inhalations/day, P = 0.0430), and reduction in mean inhalation duration (11.8 vs. 6.5 min; P < 0.0001). Greater increases in daily proportions of complete inhalations were observed in older patients (≥ 65 vs. < 65 years) and those receiving more (3 vs. < 3) concomitant PAH medications. Switching from V10 to V20 iloprost formulation significantly improved inhalation behavior in patients with PAH and may facilitate improved adherence to therapy.