herez some info I found about terrier's heart rate ... good luck at the vet's.
http://www.wndu.com/news/mommo/062006/mommo_50917.php
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The normal heart rate for him is 80 to 120. It was down to 36,” said Jan Guy, Zack’s owner. “The pacemaker is in his back right there. It's about the size of a silver dollar.”