The medical term means that a person's resting heart rate is below 60 beats per minute. There are two main types of bradycardia—sinus bradycardia and heart block. Sinus bradycardia is a resting heart rate of under 60 beats per minute that arises from the sinus node, which sets heart rhythm.

Sinus bradycardia is a type of slow heartbeat. A special group of cells begin the signal to start your heartbeat. These cells are in the sinoatrial (SA) node. Normally, the SA node fires at about 60 to 100 times per minute at rest. In sinus bradycardia, the node fires less than 60 times per minute.