Abstract Background Calcific aortic valve disease is the 2nd most frequent cause of open heart surgery. The valve interstitial cells (VIC) are crucial for calcification. SNF472 (a derivative of phytic acid) is a calcification inhibitor currently in clinical development for the treatment of cardiovascular calcification (Phase 2 CaLIPSO trial, EudraCT 2016–002834–59). SNF472 has been shown to inhibit vascular calcification in several preclinical models. Purpose 1. Establish a new model of calcification in cultured human VIC; 2. Investigate whether SNF472 would inhibit calcification in this model, and 3. Study if SNF472 might inhibit ongoing calcification processes. Methods Healthy and calcified aortic valves were obtained from heart transplant recipients and patients undergoing aortic valve replacement due to calcific valve disease, respectively. VIC were isolated and seeded in basic growth medium, osteogenic differentiation medium (Osteodiff) alone, and with addition of different concentrations of SNF472. The following series of studies were performed: 1. VIC from healthy and calcified valves were cultured for three weeks with Osteodiff; 2. VIC from calcified valves were cultured for 3 weeks in Osteodiff media with 0, 1, 3, 10, 30, or 100 μM SNF472; 3. VIC from calcified valves were cultured for 3 weeks in Osteodiff media in total, but after 1 or 2 weeks 30 or 100 μM SNF472 was added to the cultures (n=8). Calcification was visualized by Alzarin Red staining and quantified by spectrophotometry. Statistics analysis was performed nonparametric One-Way ANOVA (Friedman and Kruskal–Wallis tests) with Dunn's post-test. Results Calcification was found to be 30% stronger in cultures of VIC from calcified valves as compared to cultured VIC from healthy valves (p=0.03). SNF472 successfully inhibited VIC calcification in a dose-dependent manner. SNF472 concentrations of 1, and 3 μM inhibited calcification by 7% (not significant) and 66% (p=0.08) respectively. Concentrations of 10, 30, and 100 μM completely inhibited calcification. 30 and 100 μM of SNF472 added after 1 week reduced ongoing calcification by 84% (p<0.01) and 100% (p<0.01) respectively. When given after 2 weeks of ongoing calcification non-significant inhibition was still observed (21 and 30%, respectively). Conclusions VIC from calcified valves have a more pro-calcification phenotype than VIC from healthy valves. SNF472 is able to inhibit the development VIC calcification in vitro. By early intervention SNF472 is also able to stop the progression of ongoing calcification. SNF472 shows to be a promising therapy to treat heart valve calcification. Acknowledgement/Funding EC FP7 (GA 609020), Balearic Islands Government grant (ES01/TCAI/41_2017), FEDER 2014-2020, Laboratoris Sanifit, Palma, Spain; University of Oslo