Longer observation periods have been proven to increase the diagnostic value of Holter ECG monitoring for paroxysmal atrial fibrillation mainly. The aim of this work was to study the diagnostic efficacy of a long-term ECG monitoring in detecting various types of arrhythmias and to assess the uneven distribution of arrhythmias over different observation days. In this study 27 patients were examined, including 13 men and 14 women with a mean age of 42.8 ± 10.8 years, their complaints suggesting various types of tachy- and bradyarrhythmias. Compact recorders and original software were used. ECG recording time was 5-7 days. Using quantity criteria characterizing the level of uneven inter-day distribution of arrhythmias, advantages of long-term observations over a 24-hour monitoring were confirmed for such arrhythmias as sinus pauses over 2.5 seconds, a second degree AV block, paroxysmal supraventricular tachycardia, single and paired ventricular extrasystoles, ventricular salvos, ventricular tachycardia.