Several five-ringed heterocyclic oligomers (containing thiophene and pyrrole units) have been studied by cyclic voltammetry and double-step chronoamperometry in dichloromethane. The variation of the redox potentials with the substitution has been correlated with both electronic and steric effects. Most of the compounds studied have been found to electrodimerize by a cation radical-cation radical dimerization mechanism, and the corresponding rate constants have been extracted. In addition, it has been thoroughly discussed whether a possible slow deprotonation step following the irreversible dimerization step would affect the determination of the rate constants and also its possible effects on the apparent number of electrons exchanged per oligomer.