The Sympathetic Nervous System (SNS) releases the hormones (catecholamines-epinephrine and norepinephrine) to accelerate the heart rate. The Sympathetic Nervous System (SNS) is a part of the Autonomic Nervous System (ANS), along with the Parasympathetic Nervous System (PNS). The SNS activates what is often termed as the body's fight or flight response (during emergency situations).