Heart; conduction system. 1. SA node. 2. AV node. 3. Bundle of His. 8. Septum
Ventricular fibrillation (VF) showing disorganized electrical activity producing a spiked tracing on an electrocardiogram (ECG)
Overview of the system of electrical conduction which maintains the rhythmical contraction of the heart
Broad classification of arrhythmias according to region of heart required to sustain the rhythm
3D rendering showing thick myocardium within the heart wall.
Normal sinus rhythm, with solid black arrows pointing to normal P waves representative of normal sinus node function, followed by a pause in sinus node activity (resulting in a transient loss of heartbeats). Note that the P wave that disrupts the pause (indicated by the dashed arrow) does not look like the previous (normal) P waves – this last P wave is arising from a different part of the atrium, representing an escape rhythm.
The swirling musculature of the heart ensures effective pumping of blood.
Principle of ECG formation. Note that the red lines represent the depolarization wave, not bloodflow.
Cardiac muscle
Different wave shapes generated by different parts of the heart's action potential
Illustration of a cardiac muscle cell.
Intercalated discs are part of the cardiac muscle cell sarcolemma and they contain gap junctions and desmosomes.
Dog cardiac muscle (400X)

The electrical conduction system of the heart transmits signals generated usually by the sinoatrial node in the heart to cause contraction of the heart muscle.

- Electrical conduction system of the heart

Dysfunction of the conduction system can cause irregular heart rhythms including rhythms that are too fast or too slow.

- Electrical conduction system of the heart

Arrhythmias are due to problems with the electrical conduction system of the heart.

- Arrhythmia

Each cardiomyocyte needs to contract in coordination with its neighboring cells - known as a functional syncytium - working to efficiently pump blood from the heart, and if this coordination breaks down then – despite individual cells contracting – the heart may not pump at all, such as may occur during abnormal heart rhythms such as ventricular fibrillation.

- Cardiac muscle

Other potential roles for fibroblasts include electrical insulation of the cardiac conduction system, and the ability to transform into other cell types including cardiomyocytes and adipocytes.

- Cardiac muscle

Automaticity refers to a cardiac muscle cell firing off an impulse on its own.

- Arrhythmia
Heart; conduction system. 1. SA node. 2. AV node. 3. Bundle of His. 8. Septum

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Image showing the cardiac pacemaker or SA node, the normal pacemaker within the electrical conduction system of the heart.

Cardiac pacemaker

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Image showing the cardiac pacemaker or SA node, the normal pacemaker within the electrical conduction system of the heart.
Schematic representation of the sinoatrial node and the atrioventricular bundle of His. The location of the SA node is shown in blue. The bundle, represented in red, originates near the orifice of the coronary sinus, undergoes slight enlargement to form the AV node. The AV node tapers down into the bundle of HIS, which passes into the ventricular septum and divides into two bundle branches, the left and right bundles. The ultimate distribution cannot be completely shown in this diagram.

The contraction of cardiac muscle (heart muscle) in all animals is initiated by electrical impulses known as action potentials.

Sometimes an ectopic pacemaker sets the pace, if the SA node is damaged or if the electrical conduction system of the heart has problems.

Cardiac arrhythmias can cause heart block, in which the contractions lose any useful rhythm.