Receptors Mediating Sympathetic Activity in the Heart

In humans, the autonomic nervous system plays a critical role in regulating involuntary physiological functions, including heart rate and digestive processes. The autonomic nervous system consists of sympathetic and parasympathetic divisions, which often have opposing effects on various target organs. For instance, the sympathetic nervous system typically prepares the body for 'fight or flight' responses, while the parasympathetic nervous system promotes 'rest and digest' functions. A patient in a medical scenario has presenting symptoms of rapid heart rate and increased sweating in a non-stressful environment, suggesting increased sympathetic activity.

Based on this information, which of the following receptors in the heart would most likely mediate these symptoms?