Abstract The work developed and presented in this thesis continues the research line started with another PhD. thesis entitled ”Estudio de métodos para procesamiento y agrupación de señales electrocardiográficas”. The algorithms and methods used here have been developed to automatically process the information contained within a special kind of long-time electrocardiographic registers (called Holter ECG). The aim of the work is to provide doctors and cardiologists with a complete set of tools that make them easier the task of analysing and diagnosing the cardiac diseases. To perform this, we will apply to the Holter ECG a clustering process in order to automatically group the heart beats that compose the signal into a very few clusters from where doctors, by means of the manual inspection of a representative beat from each cluster, easily and quickly provide a diagnosis. Finally, to achieve the clustering objective, we will study the ECG morphological features using the large amount of databases available through the internet, the development of new ECG signal applications, the comparison among methods, and some algorithm optimization tasks have been also performed. A polygonal approximation algorithm used for ECG compression, the Principal Component Analysis (PCA) scheme applied to the feature selection stage or heart beat modelling by means of the Hidden Markov Models (HMM) for feature reduction too. The application of all the methods described above has become an improvement of the final Holter ECG clustering process.