a once - a - day controlled release diltiazem formulation is described which includes : from 20 to 50 % by weight of enteric polymeric membrane coated pellets comprising a polymer membrane coated core which comprises a biologically inert core which is coated with a first layer which consists essentially of diltiazem and a polymeric binder ; and a second layer which comprises a membrane comprising a ph dependent polymeric material ; and from 50 % to 80 % by weight of delayed pulse polymeric membrane coated pellets comprising a polymeric membrane coated core which comprises a biologically inert core which is coated with a first layer which consists essentially of diltiazem and a polymeric binder and a second layer which comprises a polymeric membrane which will substantially maintain its integrity in the varying ph conditions of the gastrointestinal tract but is permeable to diltiazem ; and a unit dose containment system .