ObjectiveMacrophages have been described in calcific aortic valve disease, but it is unclear if they promote or counteract calcification. We aimed to determine how macrophages are involved in calcification using the Notch1 +/model of calcific aortic valve disease. Approach and ResultsMacrophages in wild-type and Notch1 +/murine aortic valves were characterized by flow cytometry. Macrophages in Notch1 +/aortic valves had increased expression of MHCII. We then used bone marrow transplants to test if differences in Notch1 +/macrophages drive disease.Notch1 +/mice had increased valve thickness, macrophage infiltration, and M1-like macrophage polarization regardless of transplanted bone marrow genotype. In vitro approaches confirm that Notch1 +/aortic valve cells promote macrophage invasion as quantified by migration index and M1-like polarization quantified by Ly6C and CCR2 positivity regardless of macrophage genotype. Finally, we found that macrophage interaction with aortic valve cells promotes osteogenic, but not dystrophic, calcification by decreasing abundance of the STAT3β isoform. ConclusionsThis study reveals that Notch1 +/aortic valve disease involves increased macrophage recruitment and polarization driven by altered aortic valve cell secretion, and that increased macrophage recruitment promotes osteogenic calcification through STAT3 splicing changes.Further investigation of STAT3 and macrophage-driven inflammation as therapeutic targets in calcific aortic valve disease is warranted.