Epinephrine, more commonly known as adrenaline, is a hormone secreted by the medulla of the adrenal glands. Strong emotions such as fear or anger cause epinephrine to be released into the bloodstream, which causes an increase in heart rate, muscle strength, blood pressure, and sugar metabolism. the startle effect releases substances in the body such as adrenaline which cause the heart rate to increase and the heart to beat more vigorously, creating a sensation of panic, heart pounding and heart racing. This is the experience of becoming aware of a natural or normal functioning of the nervous system.
It looks like some people are more prone to the effect of adrenaline to cause them tachycardia or/and palpitation , the underlying bio-molecular reasons for that difference are missing for me, what makes some people more sensitive to it. is it a sensitivity in their sympathetic nervous system ? is it some receptors on the heart-cells wall ? what are the details of that and were to learn more about it
Source : "https://www1.udel.edu/chem/C465/senior/fall00/Performance1/epinephrine.htm.html#:~:text=Epinephrine&text=Epinephrine%2C%20more%20commonly%20known%20as,blood%20pressure%2C%20and%20sugar%20metabolism."