Many times, bradycardia is caused by a problem with the heart's sinoatrial (SA) node. This so-called "natural pacemaker" is a cluster of cells in the right atrium that sends electrical signals to help control the heartbeat. An SA that does not work properly can cause the heart rate to slow down, speed up or become inconsistent. Sometimes, a pacemaker is required. A pacemaker that detects bradycardia sends a signal to the heart that restores a healthy rate.