Sinus rhythm

[2] On the electrocardiogram (ECG), a sinus rhythm is characterised by the presence of P waves that are normal in morphology.

[2] The term normal sinus rhythm (NSR) is sometimes used to denote a specific type of sinus rhythm where all other measurements on the ECG also fall within designated normal limits, giving rise to the characteristic appearance of the ECG when the electrical conduction system of the heart is functioning normally; however, other sinus rhythms can be entirely normal in particular patient groups and clinical contexts, so the term is sometimes considered a misnomer and its use is sometimes discouraged.

Sinus rhythms may be present together with various other cardiac arrhythmias on the same ECG.

[2] This means that the P wave should be: If the P waves do not meet these criteria, they must be originating from an abnormal site elsewhere in the atria and not from the sinus node; the ECG cannot, therefore, be classed as showing a sinus rhythm.

Exceptions to this include complete heart block and certain ventricular artificial pacemaker rhythms, where the P waves may be completely normal in shape, but ventricular depolarization bears no relation to them; in these cases, the speed of the "sinus rhythm of the atria" and the speed of the ventricular rhythm must be calculated separately.