Measurement of physical activity among patients with heart failure typically requires a special approach due to the patients' physical status. Nowadays, a technology is already available that can measure the kinematic movements in 3-D by a pacemaker and implantable defibrillator giving an assessment on software. The telemetry data can be transmitted to a central system. The research aims to elaborate the methods that help to compare of the data concerning physical activity both built-in an accelerometer in Cardiac Resychrinisation Therapy (CRT) devices and data obtained from an external Actigraph GT3XE-Plus Triaxial Activity Monitor. 5 persons participated in the pilot study (n = 5); mean age: 57 ± 13.37; BMI: 90.6 ± 7.63. The Actigraph data from CRT device were examined in a 6-day-interval, between February 28 and March 5, 2014. The investigation started conducting a 6-minute walking test and continued with the measurement of daily physical activity. For data analysis descriptive statistics and linear regression analysis were used. It is clear from the data obtained from Actigraph that the MET values (mean: 1.17 ± 0.096) of the patients in the sample were extremely low due to their disease. However, some patients with higher physical activity than average (1.26; 1.28) seemed to be noteworthy, but they showed lower performance than healthy people. The physical activity of the patients during the 6-minute walking test corresponded to 1.9-2.48 MET. The physical activity of patients was found typically in the "light or moderate range" classifying the physical activity by Actigraph. Data from Actigraph are accurate and detailed making the physical activity of the patients measurable and appreciable. The results of the 6-minute walking test were in the category from moderate to very vigorous for individualized moderate physical performance based on Actigraph. It indicates the individual performance differences among patients. However, the daily physical performance is even lower than that of the 6-minute walking. We can conclude from the data related to the percentage of the average activity in CRT system to the average energy consumption and the improvement in the patients' physical condition. Due to the limitations of the sampling frequency the different time intervals cannot be isolated in the different intensity ranges. Therefore, the percentage of the data of physical activity provided by the device may have a limited use.