Any variation of the heart’s normal rhythm is considered an arrhythmia. An example of a regular variation, associated with respiratory activity, is sinus arrhythmia. Examples of irregular variations include premature contractions (PVCs), heart block, flutter, fibrillation and other ectopic beats. Rapid arrhythmias are termed tachycardias while slow arrhythmias are termed bradycardias. The image below shows the effect of PVCs on the cardiograph (top) and photoplethysmograph (bottom) tracings.