The heart normally has an innate coordinated impulse conducting system which results to its contraction at regular intervals. The sinoatrial node (SA) is mainly responsible for this normal rhythm that is why it is called the pacemaker of the heart. The normal heartbeat is 60-100 beats per minute. This means that the SA node sends impulses and thereby makes the heart contract 60-100x per minute. Atrial fibrillation is a condition wherein the impulse conducting system is erratic hence its contraction will not be coordinated. The result will be contraction happening at irregular intervals resulting to an irregular rhythm. Atrial tachycardia is a condition wherein an ectopic pacemaker is dominating over the SA node; the heart still contracts at regular intervals but beats very fast, usually >100 beats per minute and can reach 140-200 beats per minute. This is an emergency and medications should be given promptly to avoid serious, life-threatening consequences. I hope I have answered your question and take care always.
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