The electrocardiogram (ECG) is a record of the heart’s electrical activity. Typical parts of an ECG signal are: P wave, QRS complex and T wave. Detection of these characteristic parts of the ECG signal is an important factor for the study of heart functions. This paper presents the basics of heart anatomy and explains the electric activity of the heart. The basic steps of implementing most algorithms for detecting characteristic ECG waves are briefly described. Phasor transformation as a method of signal analysis is described and an algorithm for detecting characteristic parts of ECG is developed. Phasor transform was used for signal processing. The most important bases of ECG signals for testing algorithms of detection characteristic ECG waves were presented and a comparison of P waves annotations for 12 signals taken from MIT-BIH arrhythmia signal base in relation to Elgendi's P wave annotation record was performed. After that, the algorithm was tested on standard ECG signal bases for arrhythmia, MIT-BIH and QT signal base. The success of the algorithm was estimated by calculating the sensitivity (Se) and positive predictivity (P+) with an allowable error interval of 150 ms between the annotations and the detected positions of the peak of characteristic waves. After that, a comparison of the sensitivity for different error intervals over the signals from the MIT-BIH and QT signal base was performed. An algorithm is implemented within Matlab programming environment.