The research of the individual peculiarities of the medications' influence on a human organism is an important factor of the treatment of various diseases. Such researches are conducted at the stage of in-depth clinical tests and continued after the medication is allowed for general use. Much emphasis is put on the elaboration of a sensitive and selective method of determining the concentration of the medication in biological objects. The electrochemical methods proved to be very effective in determining the presence of medications and toxins, as well as their metabolites in biological matrixes. One of them is the method of inversional voltamperometry (IVA), which combines sensitivity with selectivity, and tacks the complicated character of the preliminary sample processing.Quantitative determination of digoxin and cordanum is a matter of current interest in evaluating the effectiveness of treating cardiovascular diseases.