Many alternative shift schedules "compress" the working week into a smaller number of days by adding more work hours per day. The assessment of such work schedules needs to take into consideration the advantages and disadvantages of this style of work on workers' health and well-being. The aim of the present study was to evaluate the cardiovascular strain in control room operators in a chemical plant working on an extended workday schedule and to assess their tolerance to the longer shifts. The cardiovascular strain of the operators (11 males and 10 females) was evaluated by ECG Holter monitoring during both the 12-hour day and night shifts. The results obtained indicate a light to moderate cardiovascular strain in the male operators. The higher work heart rate (HR) and more pronounced ECG changes (frequent HR peak values, transient ST-depressions, etc.) indicate a higher level of cardiovascular strain in the female group during the day shift. During the night shift the mean HR values were significantly lower in both groups. At night the HR of the male operators displayed a well expressed circadian rhythm while we observed a flattening of the HR variations in the female group. The results of the job analysis, the time-budget survey and the data obtained by the ECG Holter monitoring indicate in general that the cardiovascular strain in this occupation is acceptable and the chemical operators' job is suitable for a longer shift duration. Nevertheless a need for the improvement of the working conditions and organization, especially for the female operators, is apparent.