This is the most common rhythm disturbance of the heart, and it includes a variety of arrhythmias. In technical terms, it is called supraventricular tachycardia. Supraventricular is a description of the part of the heart composed of the upper chambers (atria), while the rest of the heart's lower chambers (ventricles). Tachycardia means that the heart beats rapidly, the pulse is high if the heartbeat is too fast (less than 200 beats per minute), the atrium and ventricle usually close in the normal sequence (upper chambers first, then the heart chambers). Such a condition can be uncomfortable but is very rarely dangerous. Transient attack with such a rapid heart rate is also called paroxysmal supraventricular tachycardia.
It is important that the heart chambers and upper chambers are synchronized, meaning that they turn in the same rhythm. If the upper chambers pumps very quickly, at some arrhythmias may be difficult for the chambers of the heart to keep up.
Then the situation arises that the two part of the heart is working independent of each other and do not follow the same rhythm. If that happens, the heart pumps less efficiently, and it may be necessary treatment to restore a common rhythm. Atrial fibrillation and atrial flutter are examples of such a state.