An interstitial cell that is part of a cardiac valve leaflet. Along with valve endothelial cells, a valve interstitial cell maintains tissue homeostasis for the function of cardiac valves through secreting biochemical signals, matrix proteins and matrix remodeling enzymes. [ https://orcid.org/0000-0001-7655-4833 https://doi.org/10.1161/ATVBAHA.120.314789 http://www.ncbi.nlm.nih.gov/pubmed/25311230 https://doi.org/10.1098/rsif.2017.0580 https://doi.org/10.2353/ajpath.2007.070251 https://doi.org/10.1161/JAHA.117.006339 ]