What happens when the electrical impulse reaches the Purkinje fibers?

When the electrical impulse reaches the Purkinje fibers, it triggers the contraction of the ventricles. The Purkinje fibers are part of the electrical conduction system of the heart and are responsible for rapidly transmitting the impulse to the ventricular myocardium. This efficient spread of the impulse leads to a coordinated contraction of the ventricles, allowing them to effectively pump blood out of the heart—into the pulmonary artery and aorta.

By the time the signal reaches the Purkinje fibers, the atria have already contracted, having received the impulse earlier via the atrioventricular (AV) node and bundle of His. Therefore, the primary function of the Purkinje fibers is to ensure that the ventricles contract in a synchronized manner for optimal blood ejection. Other options such as a decrease in heart rate or blood vessel dilation do not directly relate to the role of the Purkinje fibers in the conduction system and ventricular contraction.