In human body, the hormone which is secreted into blood and which controls the rate of heart beat is

Adrenaline (also known as epinephrine) is the hormone secreted into the blood by the adrenal medulla to control the rate of heart beat [1]. It is primarily released during stressful or exciting situations as part of the 'fight or flight' response. When adrenaline acts on its target organs, specifically the heart, it causes the heart to beat faster to increase the supply of oxygen to the muscles [3]. While other hormones like thyroxine regulate the general metabolic rate [4] and insulin regulates blood sugar levels [3], adrenaline is the specific hormone responsible for the rapid increase in heart rate and blood pressure to prepare the body for immediate action [3]. This hormonal control works alongside the nervous system to coordinate the body's response to external stimuli [2].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 6: Control and Coordination > 6.3 HORMONES IN ANIMALS > p. 109
2. [3] Science , class X (NCERT 2025 ed.) > Chapter 6: Control and Coordination > Do You Know? > p. 110
3. [4] https://www.ncbi.nlm.nih.gov/books/NBK613062/
4. [2] Science , class X (NCERT 2025 ed.) > Chapter 6: Control and Coordination > Do You Know? > p. 111