Healthy people have a normal heart rhythm. Like many other things in medicine, normal simply means what is found most commonly in the average person of the same age and size. For most adults, the normal heart rhythm originates in the sinus node of the heart at a regular rate of 60 to 99 beats per minute. The sinus node is the heart’s own natural pacemaker. It is designed to start each heartbeat and is closely regulated by the central nervous system. Because the signal starts in the sinus node, the normal rhythm of the heart is called the sinus rhythm.
If the rate of the sinus rhythm is normal, it is usually called a normal sinus rhythm.
If the heart rate is faster than 100 beats per minute, it is usually called sinus tachycardia (tachy – fast/cardia – heart). Sinus tachycardia is what happens normally with exercise as the heart speeds up. Conditions like fever and illness can also cause it.
If the heart rate is below 60 beats per minute, it is referred to as sinus bradycardia (brady – slow/cardia – heart). Sinus bradycardia can happen when we relax or sleep, and in very well-trained athletes when they are at rest as a result of increased vagal tone on the heart.
If the sinus heart beat is irregular, it is called sinus arrhythmia. A sinus arrhythmia can happen as the result of lung expansion and relaxation on the heart, which is what happens with normal breathing. Sinus arrhythmia can be especially noticeable in people with lung disease like asthma and COPD.« Back to Glossary Index