Artificial cardiac pacemakers are most commonly used in the management of symptomatic bradycardias. These pacemakers provide electrical stimuli to the atria or ventricles or both at a desired rate to cause them to contract regularly at that rate. On the electrocardiogram, these electrical impulses are seen as "pacemaker spikes" identified by their abrupt vertical spike (arrows below), preceding the atrial or ventricular complex, depending on which chambers the pacemaker is responsible for. In this example, a pacemaker has been inserted which is responsible for providing a regular ventricular rhythm (wide, bizarre QRS complex - circled below). No atrial contractions are present.