Enoximone and piroximone are cardiotonic agents for use in patients with congestive heart failure. Electroanalytical studies revealed that the dihydroimidazolone functionality was oxidizable and that this property can be analytically useful. The compounds undergo a two-electron, irreversible oxidation in neutral to acidic media, leading to two major products. Results in basic media show up to three electrons transferred per molecule and much higher oxidation potentials at the fresh carbon paste electrode than at identical electrodes preconditioned in supporting electrolyte at +1.2 V. Use of amperometric detection with HPLC provides excellent measurement sensitivity (less than 1 ng) and reproducibility. Carbon paste and glassy carbon electrodes surfaces are not obviously affected by the electrochemical reactants or products. Piroximone, in addition, contains a 4-pyridoyl function which is irreversibly reducible at a mercury electrode, with excellent response linearity, and measurement sensitivity to at least 10(-7) M by differential pulse polarography.