This paper aims to evaluate the cardiovascular response to exercise in young and master athletes. The study involves comparison with control groups of untrained subjects of the same age. The paper describes in particular the processing methods and results concerning the ECG signals collected during exercise test. Methods include PNN calculation, Multiscale Entropy analysis (MSE), and a comparison between clustering and an Artificial Neural Network analysis performed by means of chaotic attractors. The analyses carried out lead to a good stratification of the subjects, especially in terms of the MSE1 variable. Future developments are underway supported by many other diagnostic tests administered to the same subjects.