The objective of this study was to compare the in vivo characteristics of diltiazem extended release formulations for once daily, which were expected to be bioequivalent. Either two capsules of a test formulation or a 1 of the reference formulation, both containing 360 mg diltiazem were administered to healthy male volunteers after keeping fast of ten hour in a randomized, open label,three period crossover design. Plasma samples obtained over the subsequent period of 72 hours were analyzed using a validated LC-MS/MS method. Safety profile and tolerability of the study medications were assessed by analysis of adverse events obtained by vital sign measurements, electrocardiography, and clinical. The 90% CI for the log transformed data for Cmax, AUC0-t,AUC0-∞ for both the test product fell in the prescribed limits of bioequivalence for narrow therapeutics index drugs i.e. 80 to 120%. This single dose study found that the test and reference products met the regulatory criteria for bioequivalence in healthy, male volunteers under fasting.