An electrocardiogram (ECG) is a test that is commonly used to assess the heart. Your dog’s heart beats because of an electrical impulse passing through the heart causing it to contract and pump blood. This impulse passes through the heart in a predictable manner that can be traced on an ECG recording.

By analyzing the electrical impulses passing through the heart, abnormalities within the heart can be found. These abnormalities may include issues such as arrhythmias (irregular heartbeats), abnormalities in the size and structure of the various heart chambers, abnormal conduction, and other defects of the heart.

In most cases, an ECG can be performed in your veterinarian's office as an outpatient visit. No special preparation is typically required for this procedure.

Your dog will be required to remain still for this test, either standing or laying down on an examination table. The ECG electrodes are applied to your dog's skin, at the base of each of his four legs. Rubbing alcohol or a special conduction gel may also be applied to help the electrical impulses travel more easily from your dog's body into the ECG electrodes.

"In most cases, an ECG can be performed in your veterinarian's office as an outpatient visit."

Once the electrodes are applied, your dog will be kept still for a brief period of time, in order to allow the ECG to record the electrical impulses passing through the heart. Your dog's electrical conduction may be traced for less than a minute or for several minutes, depending on what abnormality your veterinarian suspects and how effectively your dog is able to remain still for a high-quality ECG recording. After the test is run, it may be interpreted in-house by your veterinarian or it may be sent out to a veterinary cardiologist for interpretation.

In some cases, the ECG machine may be attached to your dog and left in place for 24 hours or more. This test, called a Holter Monitor, can help your veterinarian detect arrhythmias that occur uncommonly. See handout "Holter Monitor in Dogs" for more information.

An ECG is often a component of the workup for any dog suspected of having heart disease. Clinical signs of heart disease that you may see at home, which might indicate a need for an ECG, can include any of the following:

• weakness
• lethargy
• exercise intolerance
• shortness of breath
• coughing

Even if your dog is not showing signs of heart disease at home, your veterinarian may also recommend an ECG if your dog has physical exam findings that are suggestive of heart disease. These findings may include:

• an irregular heartbeat
• a heart murmur (which indicates turbulent blood flow over a valve within the heart)
• irregular pulses
• abnormal lung sounds

An ECG may also be performed as a screening test in geriatric dogs or dogs that are undergoing anesthesia. Additionally, ECG monitoring is common in dogs of any age when they are under general anesthesia.

An ECG can provide your veterinarian with a variety of information about your dog's heart function.

1. Is the heart rate normal? An ECG allows an accurate determination of your dog's heart rate. This can reveal whether his heart is beating at a normal pace, or beating too quickly or too slowly. An elevated or decreased heart rate can suggest medical issues that may warrant investigation.
2. Is the heart rhythm normal? An ECG provides a very accurate way for your veterinarian to assess your dog's heart rhythm. If his heart rhythm is abnormal, analysis of the ECG results can diagnose the exact arrhythmia that is present and suggest likely underlying causes for this arrhythmia.
3. Does the dog's heart size appear to be normal? An ECG measures electrical conduction through the heart. Enlarged heart tissue conducts electricity differently than normal heart tissue; therefore, an ECG can sometimes suggest abnormalities in the size of specific heart chambers.  While this determination is not completely accurate or reliable, it can suggest the need for further investigation via radiographs (X-rays) or echocardiography (an ultrasound of the heart).