Faulty electrical signaling in the heart causes arrhythmias. A pacemaker uses low-energy electrical pulses to overcome this faulty electrical signaling. Pacemakers can: speed up a slow heart rhythm, help control an abnormal or fast heart rhythm, make sure the ventricles contract normally if the atria are quivering instead of beating with a normal rhythm (a condition called atrial fibrillation), coordinate the electrical signaling between the upper and lower chambers of the heart, coordinate the electrical signaling between the ventricles. Pacemakers that do this are called cardiac resynchronization therapy (CRT) devices. Pacemakers also can monitor and record your heart's electrical activity and heart rhythm. Newer pacemakers can monitor your blood temperature, breathing rate, and other factors and adjust your heart rate to changes in your activity.