Purkinje fibers are special fibers that are located in the atrioventricular, or AV, bundle of the heart. Their function is to send nerve impulses to the cells in the ventricles of the heart and cause them to contract and pump blood either to the lungs or the rest of the body.
The AV bundle itself is found in the heart's septum, which is the wall that divides the right and left chambers of the heart. It sends impulses down the septum through the AV bundle branches to the Purkinje fibers.
The Purkinje fibers can be found in the ventricle walls, which are at the bottom of the heart in an area called the subendocardium. They're made up of specialized cardiomyocytes, which are the cells that make up cardiac muscle. These special cells found in the Purkinje fibers are able to conduct nerve signals more rapidly than other muscle cells in the heart and so are crucial for the normal beating of the heart. They are able to send signals at speeds of between 3 and 12 feet per second. However, the Purkinje fibers do not actually set the heart rate.
The fibers were discovered by Jan Evangelista Purkyne, a Czech physiologist, in 1837.