The (−) epicatechin (Epi) is a flavonoid with antioxidant and regenerative properties for cardiac tissue. In this work, a study of release assays and their corresponding adjustments to models was performed to determine the mechanism of (−) Epi release in the cellulose acetate (CA)–polyvinylpyrrolidone (PVP) system. The morphology of the material was considered, fibers, or spheres, as well as the possible chemical interactions between Epi, PVP, and CA. It was observed that in the systems in which the PVP is present, a high release is observed in comparison with those that only contained CA and (−) Epi, which showed very low release. This difference can be explained considering the possible hydrogen bond interaction between CA and (−) Epi, as well as the insolubility of the CA, in the release medium. The factors that have an important effect on the release of (−) Epi in the different systems are: the morphology, a faster release in morphologies with greater surface area, and the chemical interactions that can be formed among the (−) Epi and the components of the matrix. Another factor is the solubility of the components in the release medium, which allows the diffusion and drag phenomena to be observed simultaneously. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47166.