Does an elevated hgb cause tachycardia?

No: However, the usual cause of a mildly elevated hemoglobin is dehydration and this may cause tachycardia.

Hgb and heart rate: High hemoglobin should not in general cause tachycardia. One way it could cause tachycardia is if you are dehydrated and so the high hemoglobin is artificial. In that case the tachycardia is due to the dehydration and drinking fluids will help. Also high HGB (polycythemia vera) makes the blood thick and you can feel short of breath which can then indirectly cause your heart rate to go up.