Breathing Question

Just curious, does anyone know how often a horse inhales/exhales at the trot? I'm asking because I was riding my horse the other day and noticed I could hear him breathing at the trot. I wouldn't say it was labored, but it was a noticeable sound. While we were trotting, it would be two beats silence, two beats sound, repeat. I'm pretty sure it was the inhale part that I was hearing. Is that the normal trotting inhale/exhale breathing rate? I get a little nervous because my horse has a heart murmer. Anytime I hear anything breathing related, I just take more seriously than I probably need to.

I know that while cantering, the horse inhales and exhales in time with the gait; breathing in as they lift up, out as the come back down. It seems reasonable for a horse to do something similar in the trot.

Since your horse has that murmur, I wouldn't just wave it off. If his breathing is regular, that's a good sign, and if it comes back down to his resting rate in a normal amount of time, that's also a good thing. Regardless, I would still call a vet and ask. The heart isn't something to mess around with.