This paper proposes a mathematical model for generating synthetic artificial ECG signal based on geometrical features of a real ECG signal. By variation of its parameters each particular wave of PQRST complex can be adjusted as needed allowing the generation of arbitrary ECG patterns typical for diseases and arrhythmia. The input parameters are treated to avoid mixing order of PQRST waves in case of automatic parameter variation and allow generating different patterns for each subsequent heartbeat independently. Each particular wave is modelled using an elementary trigonometric function or a Gaussian monopulse. Including possible addition of equipment noise as well as respiration frequency such an artificial signal can be used as a test signal for some signal processing methods. The model was tested by comparison of synthetized patterns against patterns generated by LabVIEW Biomedical Toolkit, while the parameters of model are found using the differential evolution algorithm