This study aims to compare the effects of upfront combination therapy with tadalafil and ambrisentan in PAH-SSc on PVR and RV mass. It will also assess novel markers of RV function by cardiac MRI and echocardiography, as well as the conventional endpoints, including 6 MWD and functional class. The trial is unique in that it will enroll only PAH-SSc patients, the PAH subgroup with the poorest outcomes and will be considerably longer in duration (36 weeks) than previous studies.