Early detection of mild pulmonary arterial hypertension (PAH) based on clinical evaluation and echocardiography remains quite challenging. In addition to enhanced right ventricular (RV) assessment, cardiac magnetic resonance (CMR) imaging may accurately reflect deleterious remodeling and increased stiffness of the central pulmonary arteries based on pulsatility, or percent change of the PA during the cardiac cycle. The purpose of this study is to assess the utility of measuring PA pulsatility by CMR as a potential early maker in PAH. We hypothesize that pulsatility may help discriminate mild PAH from normal control subjects. Consecutive patients with PAH (n = 51) were prospectively enrolled to receive same day CMR and right heart catheterization (RHC). PA stiffness indices including pulsatility, distensibility, compliance, and capacitance were calculated. Comparisons were made between patients with varying severities of PAH and normal controls (n = 18). Of the 51 subjects, 20 had mild PAH, and 31 moderate-severe based on hemodynamic criteria. PA pulsatility demonstrated a progressive decline from normal controls (53%), mild PAH (22%), to moderate-severe PAH (17%; p < 0.001). There was no difference in RV size, function or mass between mild PAH and normal controls. PA pulsatility below 40% had an excellent ability to discriminate between mild PAH and normal controls with a sensitivity of 95% and specificity of 94%. CMR assessment of PA stiffness may noninvasively detect adverse pulmonary vascular remodeling and mild PAH, and thus be a valuable tool for early detection of PAH. Trial Registration: ClinicalTrials.gov Identifier: NCT01451255; https://​clinicaltrials.​gov/​ct2/​show/​NCT01451255.