As a number have already said, it may end up being nothing. However, as a frequent pulse worker I do have one caution: some murmurs play with the heart monitors. In our group we have one mare with a documented arrhythmia who cannot be taken with a monitor -- it will give you a way high number. At a ride week before last, I had several horses who with the monitors seemed to be bouncing from the 60s to 70s and back. Curious, I put the stethoscope on an in every case heard something odd that made me realize why the monitors were bouncing.
So it may never be an issue, but if you have problems with a pulse reading with a monitor, go low-tech to check for sure. Mickie