Seventy-one patients(152 times) With premature systoles were studied quantitatively for haemodynamic changes by non-invasive technique-impedance cardiography and simultaneous electrocardiography. The stroke volume (SV) of the sinus beats and premature systoles were calculated.There were no significant difference between atrial premature systoles

junct-urnal premature systoles and ventricular premature systoles on the haemodynamic changes (p>0.05). The average SV of premature systoles is 35% of sinus beats. Premature systoles less than 5 beats/min may cause and average drop of 5% of cardiac output (CO)

While the premature systoles increased to 10-20 beats/min

the CO would be dropped further of 10-19%. there Was a high linear correlation between sr of all premature systoles and the coupling interval premature systoles (p<0.05-0.001).According to the coupling interval of premature

the time percentage of R-R interval of sinus rhythm

the premature were divided into early period

middle period and late period types

≤40%

41-70% and≥71% of sinus beat rhythm R-R interval respectively. There was little SV in early period premature systoles. However average SV is 53.62% of sinus beat in late period premature systoles. It is suggested that the impedance cardiograms Would be of interest for its simplicity and noninvasion and in reliably estimating beat-by-beat of left ventricular stroke volume in humans