Normal Sinus Rhythm (NSR) is the expected rhythm on an ECG in patients without pathophysiology. It represents the normal electrical cycle of the heart, which was discovered once a tool capable of detecting it was invented: the electrocardiogram (ECG/EKG).

Sinus Bradycardia (SB) is a Sinus Rhythm with a rate less than 60bpm and is otherwise identical to Normal Sinus Rhythm (NSR). This slow rate results in long RR Intervals and fewer complexes per minute.

Sinus Tachycardia is a Sinus Rhythm with a rate greater than 99bpm and is otherwise identical to NSR. This fast rate results in short RR Intervals and more frequent complexes per length.

Supraventricular Tachycardia (SVT) is a category rather than a specific rhythm. SVTs are tachycardic rhythms which originate above the ventricles.

Atrial fibrillation is the most common non-sinus arrhythmia. It is characterized by an irregularly irregular rhythm and fibrillation waves on the baseline.

AV Pacemakers (a.k.a. Dual Chamber Pacing) artificially activates both the atria and ventricles in sequence. Sharp pacemaker spikes before both P waves and QRS complexes are indicative of AV pacing.

Ventricular Tachycardia is a potentially lethal regular wide-complex tachycardia in which the ventricles have taken over rapid pacemaking of the heart.

Ventricular Fibrillation is a lethal rhythm defined by disorganized electrical activity of the ventricles. On the ECG it creates random, erratic deflections with no discernible pattern.

Asystole is the absence of electrical activity. It creates a nearly flat EKG tracing and is considered cardiac arrest.