Normal ECG reference values in dogs (by body size) and cats

Normal ECG reference values are the expected ranges for each parameter (heart rate, P wave, PR interval, QRS complex, QT interval and mean electrical axis) in animals free of heart disease, measured in lead II at 25 mm/s and 1 cm = 1 mV. In dogs, several limits change with body size, and canine and feline values differ from each other and from human values. The number-one interpretation error is applying human reference values to dogs and cats.

Why you should not use human values

The resting heart rate of a healthy dog or cat is far higher than a human's, and the corresponding intervals are shorter. A normal cat's QT (about 0.12 to 0.18 s) would be read as dangerously short in a person, and the feline rate of 160 to 240 bpm would be tachycardia in humans. Treating these physiological differences as abnormalities produces false positives and misguided decisions.

The veterinary ECG also has technical specifics: the standard lead for measuring and calculating rate is lead II, with the animal in right lateral recumbency, and the usual calibration is 25 or 50 mm/s. Before comparing any value with the table, confirm paper speed, gain and positioning, because they directly change durations and amplitudes.

Reference table: dog vs cat

The values below draw primarily on modern veterinary electrocardiography from Santilli et al. (Electrocardiography of the Dog and Cat, 2nd ed.), measured in lead II. In dogs, some limits vary with body size and are noted within each line.

How to measure and interpret with caution

Measure durations in seconds and amplitudes in millivolts from the isoelectric baseline, always confirming the trace's speed and gain. Remember that these are population reference limits, not standalone diagnostic cut-offs: a value slightly outside the range, with no clinical signs, may reflect individual variation, an artifact or positioning, rather than disease.

The ECG should always be interpreted in the patient's context, together with the physical examination, clinical signs and, when indicated, echocardiography. The diagnostic and therapeutic decision rests with the attending veterinarian. When findings or arrhythmias are unclear, referral to a veterinary cardiologist or a specialized tele-report (telelaudo) is advisable.

From the trace to the decision with INpulse

Reliable reference ranges depend on a clean trace and consistent measurements. The connected INpulse ecosystem is built for that: the INcardio X (12-lead ECG) and the INcardio Agile (6-lead ECG) record the signal, which flows through the INpulse One platform and is stored in INcloud, with patient history and the option of a tele-report (telelaudo) by cardiologists. The same signal you compare with this table can then be reviewed by a specialist when the case demands it.

This table is educational material and does not replace clinical judgment or the reading of a qualified professional.