A total of 30 apparently healthy male pipe-rolling workers having various working conditions and no resting ESG abnormalities in cardiac arrhythmias. A continuous ECG recording was performed in all the examinees during a working day, followed by interpretation of the records separately at rest and during work and automatic calculation of heart rate per min and of the number of supraventricular and ventricular premature contractions per hour. There was a heating microclimate- and hard labour-induced increase in heart rate and the number of premature contractions, ventricular premature contractions in particular.