Well-organized but overly rapid contractions of the atrium of the heart (usually at a rate of 250-350 contractions per minute). Flutter refers to a rapid vibration or pulsation. The difference between flutter and fibrillation is that flutter is well organized while fibrillation is not. Atrial flutter is a serious and potentially unstable rhythm of [..]

an irregular heartbeat in which the upper chambers of the heart (the atria) beat rapidly but consistently

Rapid, irregular atrial contractions caused by a block of electrical impulse conduction in the right atrium and a reentrant wave front traveling up the inter-Atrial Septum and down the right atrial fr [..]

Rapid, irregular atrial contractions due to an abnormality of atrial excitation.