A low relative area change (RAC) of the proximal pulmonary artery (PA) over the cardiac cycle is a good predictor of mortality from right ventricular failure in patients with pulmonary hypertension (PH). The relationship between RAC and local mechanical properties of arteries, which are known to stiffen in acute and chronic PH, is not clear, however. In this study, we estimated elastic moduli of three PAs (MPA, LPA and RPA: main, left and right PAs) at the physiological state using mechanical testing data and correlated these estimated elastic moduli to RAC measured in vivo with both phase-contrast magnetic resonance imaging (PC-MRI) and M-mode echocardiography (on RPA only). We did so using data from a canine model of acute PH due to embolization to assess the sensitivity of RAC to changes in elastic modulus in the absence of chronic PH-induced arterial remodeling. We found that elastic modulus increased with embolization-induced PH, presumably a consequence of increased collagen engagement, which corresponds well to decreased RAC. Furthermore, RAC was inversely related to elastic modulus. Finally, we found MRI and echocardiography yielded comparable estimates of RAC. We conclude that RAC of proximal PAs can be obtained from either MRI or echocardiography and a change in RAC indicates a change in elastic modulus of proximal PAs detectable even in the absence of chronic PH-induced arterial remodeling. The correlation between RAC and elastic modulus of proximal PAs may be useful for prognoses and to monitor the effects of therapeutic interventions in patients with PH.