The effects of subchronic exposure to SO 2 (400 ppm, 3 hours per day for 28 days) on non-invasively assessed systolic time intervals were investigated in guinea pigs and compared with control exposure to air. The measurements were made regu- larly every 7th day of exposure. In the course of 28 days of the experiment a slight trend of reduction of the RR interval was found ( within the range of 253.9-211.5 ms) and an associated increase of frequency ( within the range 237-285 beats per minute). In the control group these changes did not occur. Other parameters incl. the PEP:LVET did not change significantly. The changes found in the control group did not have an unequivocal trend. No significant differences were found between the exposed and control group except the length of the cardiac cycle RR after the third week of exposure ( in SO 2 exposure 211.5 ms, i.e. 84.8% as compared with the baseline value, in controls 239.6 ms, i.e. 102.4%) and the minute heart rate after the third week of exposure (in SO 2 exposure 285 beats per minute , i.e 118.9% as compared with the baseline value, in controls 256 beats per minute, i.e. 96.9%). In the other parameters no significant changes were recorded. Subchronic expo- sure to SO 2 did not affect in guinea pigs the majority of investigated non-invasively assessed systolic time inervals, a mild effect on the heart rate can not be ruled out.

        Key words: SO 2 - subchronic exposure - cardiac function - guinea pig