The objective of this work was to study the possibility of a solid sustained-release dosage form, like a tablet, be divided without changing its release characteristics. Diltiazem hydrochloride Sustained-Release (SR) tablets with a standard groove on one face, were tested and the following dissolution parameters were evaluated: t10%, t25%, and t50% dissolution time, and dissolution efficiency at t120, and at t360. To analyze the release mechanism, several release models were tested such as Higuchi, zero order, first order, Baker-Lonsdale, Hixson-Crowell, Weibull, and Korsmeyer-Peppas. The similarities between two in vitro dissolution profiles were assessed by the difference factor (f1), the similarity factor (f2) and the Rescigno index (xi(i)). The in vitro release kinetics of diltiazem hydrochloride tablets were evaluated using USP apparatus 4. Using a one-way ANOVA (a = 0.05), statistically significant differences were found for t10%, t25%, and t50% dissolution times with a constant and with a variable pH dissolution fluid. The variation coefficient for the divisibility assay (Portuguese Pharmacopoeia VI) was lower than the limit value of 10%. The diltiazem release rate from this pharmaceutical system was not constant, and diminished with the square root of time (Higuchi model) showing that the phenomenon controlling drug release was the diffusion occurring inside the swelled polymeric matrix. Diltiazem release rate was a function of the area in direct contact with the dissolution fluid and not of the pharmaceutical matrix volume. The results obtained permit us to conclude that the division, in this case, affects the drug release characteristics.