Reasons for why a newborn would hve a rapid heart rate ?

Should be fast: Newborns should have a rapid heart rate. If other symptoms or concern for illness, should be checked out, especially for a newborn. Here is a link to the pulse at the national institutes of health. There is a table midway through the page giving normal ranges at different ages. http://www.nlm.nih.gov/medlineplus/ency/article/003399.htm.