Epinephrine increases heart rate because it increases pressure in the coronary arteries. It also affects relaxation and contraction of the smooth muscle cells in the heart and blood vessels.
The sinoatrial node of the heart has special receptors that bind with epinephrine. When epinephrine binds with these receptors, heart rate increases. The SA node is known as the natural pacemaker of the heart because it controls heart rate.
Epinephrine is a chemical produced by the adrenal glands. When someone is frightened or has an emotional response to something, the release of epinephrine increases heart rate and blood pressure, preparing the body to flee a potentially dangerous situation.