Heart rate is the speed of the heartbeat measured by the number of contractions (beats) of the heart per minute (bpm). The heart rate can vary according to the body's physical needs, including the need to absorb oxygen and excrete carbon dioxide . It is usually equal or close to the pulse measured at any peripheral point. Activities that can provoke change include physical exercise , sleep , anxiety , stress , illness , and ingestion of drugs .
The heart is a muscular organ in most animals, which pumps blood through the blood vessels of the circulatory system .  Blood provides the body with oxygen and nutrients , as well as assists in the removal of metabolic wastes .  In humans, the heart is located between the lungs, in the middle compartment of the chest .