Bradycardia in an adult is any heart rate less than 60 beats per minute (BPM), although symptoms usually manifest only for heart rates less than 50. In general, two types of problems result in bradycardias: disorders of the sinoatrial node (SA node), and disorders of the atrioventricular node (AV node). Tachycardia is a faster than normal heart rate at rest. A healthy adult heart normally beats 60 to 100 times a minute, when a person is at rest. Heart rate is controlled by electrical signals sent across heart tissues. Tachycardia occurs when an abnormality in the heart produces rapid electrical signals.

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