Pulmonary artery (PA) flow analysis is crucial for understanding the progression of pulmonary hypertension (PH). We hypothesized that PA flow characteristics vary according to PH etiology. In this study, we used 4D flow cardiovascular magnetic resonance imaging (CMR) to compare PA flow velocity and wall shear stress (WSS) between patients with pulmonary arterial hypertension (PAH) and those with heart failure with preserved ejection fraction and pulmonary hypertension (PH-HFpEF). We enrolled 13 PAH and 15 PH-HFpEF patients. All participants underwent echocardiography, 4D flow CMR, and right heart catheterization. We compared right ventricular outflow tract (RVOT) flow and main pulmonary artery (MPA) hemodynamics, including peak velocity and mean and maximum WSS, between groups. PH-HFpEF patients were older and more likely to have hypertension. PAH patients had higher mean PA pressure (47.8 ± 8.8 vs. 32.9 ± 6.9 mmHg,