This research was a quasi - experimental study that carried out, the purpose was to determine the effectiveness of injection duration on site pain intensity associated with subcutaneous heparin in patients of wards of the Hazrat Fatemeh and the Shahid Beheshtie hospital of Shiraz in 2002.

         Sample group was estimated 167 patients according to pilot study and sampling was done by continous manner. Data colloction was done by using a researcher-made checklist, consisted of section of demographic carachtristics and a section to record site pain intensity . In order to assess the site pain intensity , visual analogue scale (V.A.S) was used immediately after injection. Data analysis was done by distributional indexes and parametric (paired t-test) and Bi- parametric (Mann witney-U and kruskal wallis tests).

Results indicated the 30-seconds duration of injection resulted in significantly less site pain (P<0.001), thus mean of pain intensity at 10second duration technique (38.12 ± 35.38) was higher than that of 30 second duration injection technique (22.66 ± 30.62). There was a significant difference on site pain intensity between male and female cases , in both injection techniques (10-seconds and 30- seconds), so that mean of site pain intensity of females was more than males. Between age group and site - pain intensity was a significant difference (P<0.05) in 10-seconds
   injection technique , so there was higher pain intensity in 61-70 year age group and lower pain intensity in 17-50 year age group. But between pain intensity in different age groups there were not significant difference in 30 seconds injection technique, so approximately the mean of pain intensity in all age groups was equal .

Therefore results of this research indicated administering a subcutaneous heparin injection over longer duration reduces injection site pain specially in females.