Algebraic equations from a mathematical model to experimental data relating to venous and arterial blood (HCO3-, \({\text{P}\text{C}\text{O}}_{2}\)), cardiac output, and exhaled \({\text{V}\text{C}\text{O}}_{2}\) of a group of patients with chronic heart failure (CHF) belonging to New York Heart Association class III were applied. The aim of this study was to verify whether several measurable physiological parameters were significantly different among three different groups (CHF class III patients, a control group of the same age, and a group of young and athletic subjects) and, therefore, to verify whether the algebraic equations used were useful for objectively diagnosing patients with CHF. The comparison among the results of the three groups was extremely significant, so much to unquestionably highlight the class III CHF group compared to the other two groups and therefore allowing the CHF group to be objectively characterized both at rest and during exercise. This new diagnostic method performed a first objective pathophysiological characterization of CHF class III patients, laying the foundation for an objective classification of the four classes of CHF patients and subsequent precision medicine.