The purpose of the article is to study the algorithms of statistical and intellectual data analysis and their use for processing and analysing electrocardiograms (ECG). The methods and algorithms that form the basis of statistical data processing and analysis are considered. The research methods are based on the application of statistical methods and algorithms for the analysis and pre-processing of medical data. Pre-processing is a necessary step in data processing, which makes it possible to analyze more efficiently, build more accurate models and reduce their dimensionality. Scientific novelty. The article analyses classical statistical methods used at the first stage of data processing. Their effectiveness and necessity in medical data analysis are proved. The results of the work are demonstrated on real data processing, namely, on electrocardiogram processing. Conclusions. The application of statistical analysis methods for pre-processing medical data is considered on the example of ECG processing and analysis. The main statistical characteristics were calculated: mean, variance, standard deviation, mode, median, skewness coefficient, kurtosis coefficient, and coefficient of variation. The obtained data is used to estimate the law of data distribution, test hypotheses about the laws of distribution, and normalize data. A correlation matrix is constructed for the ECG observation matrix, eigenvalues and eigenvectors are calculated, and principal components are determined on their basis. The use of principal components makes it possible to reduce the dimensionality of the data for a deeper analysis. In this study, the amount of data was reduced by a factor of four. A discrete Fourier transform was performed. The analysis of the Fourier’s transform results made it possible to isolate high-frequency electromagnetic interference transmitted through the cable from the power supply network to the device, and the frequency of the interference was determined. Motion artefacts associated with the patient’s breathing were detected. The frequency of such interference is in the range from 1 to 4 Hz. The ECG points were classified and an ECG module was built for further analysis. The classification results made it possible to identify a set of points in the vicinity of R-peaks. This makes it possible to localize QRS complexes without using a complex mathematical apparatus. The results of medical data pre-processing allow to reduce the data dimensionality, identify the presence or absence of linear relationships, and evaluate the frequency characteristics of the data. Based on the pre-processing, it is possible to plan further research and build better models for data mining.