Your Horse's Heart

only thing stimulating her parasympathetic nervous system.
She is also breathing very slowly and deeply maybe six to eight breaths per minute and these breathing cycles are also adjusting both blood pressure and parasympathetic activity. As a result the actual effect on heart rate beattobeat sometimes adds to and sometimes subtracts from other influences. Since the input of the parasympathetic nervous system to the heart actually has a left and right branch and since those branches tend to innervate different parts of the heart there are also different options to slow down the heart and reduce cardiac output. These are by slowing down the primary pacemaker the sinus node the atrioventricular AV node which lies between the atria and ventricles in the middle of the hearts conduction system or by using both. The result is a wide variation in instantaneous heart rate and rhythm.