Which of the following hormones increases heart rate?

Adrenaline, also known as epinephrine, is a hormone produced by the adrenal glands and is well-known for its role in the body's "fight or flight" response. When released into the bloodstream, adrenaline binds to receptors on heart cells, leading to an increase in heart rate and the force of heart contractions. This response prepares the body for rapid action by ensuring that more oxygenated blood is pumped to vital organs and muscles.

In contrast, insulin is primarily involved in regulating blood glucose levels, while glucagon serves to raise blood glucose levels when they are low. Acetylcholine is a neurotransmitter that generally has a calming effect on the heart, decreasing heart rate.

Thus, adrenaline is the hormone that specifically enhances heart rate, making it the correct choice in this context.