high heart rates for no apparent reason

[Derald <hispirit@gemsi.com>]

Help!!!

Did a ride a April 4th and gave the horses a few weeks of down time. 
Took them out yesterday and their heart rates were huge from the start! 
Never could ask for a trot because the were fluxuating up down from 60
to as high as 200.  These horses never hit 200 even trotting a long
hill!  So of couse that ended our ride real fast.  This was not due to
excitement,  the horses were past the initial 2-3 mile excitement
point.  And even at that they never are over 140 at the very start of a
ride and then drop fairly quickly to under 100.  The horses were eating
and drinking as normal when they came home and today they appear fine.
Any advice.  I'm quite worried.  The monitors have new batteries and
work fine on other horses.  Any info would be greatly appreciated!!

Roxi