I guess your question is about atrial flutter and fibrillation.
The electrical impulse that signals your heart to contract begins in an area called the sinoatrial node (also called the sinus node or SA node). This helps the heart pump all the blood the body needs.
In atrial fibrillation, the electrical impulse of the heart is not regular.
•Parts of the heart cannot contract in a coordinated pattern.
•As a result, the heart cannot pump enough blood to meet the body's needs.
In atrial flutter, the ventricles may beat very rapidly, but in a regular pattern.
These problems can affect both men and women and become more common as you get older.
more information in :
1.Morady F, Zipes DP. Atrial fibrillation: clinical featuers, mechanisms, and management. In: Bonow RO, Mann DL, Zipes DP, Libby P, eds. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 9th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 40
2.Olgin J, Zipes DP. Specific arrhythmias: diagnosis and treatment. In: Bonow RO, Mann DL, Zipes DP, Libby P, eds. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 9th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 39.