Application of acetylcholine along the paravertebral ganglia will cause the heart to slow down. The paravertebral ganglia are part of the sympathetic nervous system, which is responsible for the "fight or flight" response. Normally, the sympathetic nervous system increases heart rate and blood pressure in response to stress or danger. However, when acetylcholine is applied to the paravertebral ganglia, it activates the parasympathetic nervous system, which has the opposite effect of slowing down the heart rate and promoting relaxation.