Cardiac auscultation is an important part of the physical examination. And an accurate physical examination is the principal source of information about a patient's condition. Combined with a thorough history, this information is used to guide further diagnostics.

Since you are usually the first member of the clinical team to examine the patient, it's very important for you to understand the cardiac sounds when you perform the initial evaluation. You should have no problem hearing most cardiac murmurs and relaying your findings to the doctor in an organized, concise fashion. A standard nomenclature has been developed to simplify the process, which includes a grading scale for rating murmur loudness, descriptors of murmur quality and location, and names for transient cardiac sounds. These terms are often misused, so it's important to clarify their proper usage. While we will focus on murmur and heart sounds, keep in mind that you will also need to listen for arrhythmias, some of which might be transient.

What you need

Features of a good stethoscope include short (25 inches or less) double-lumen tubing, a brass or high-quality steel head with both large and small diaphragms, and a bell. The diaphragm allows for easy auscultation of high-frequency sounds, and the bell is designed for soft, low-frequency sounds.

A separate bell side is more useful in veterinary medicine than a combined diaphragm and bell side because of the patient's hair. With the combination stethoscope head, extra pressure must be applied to "get through" the hair coat. The extra pressure allows the hair to rub on the diaphragm, making it difficult to hear the low-frequency sounds made audible by the bell.

Using the bell side requires a very light touch, as too much pressure will tense the skin, causing it to act like a diaphragm. A neonatal stethoscope is helpful with puppies and kittens. Your stethoscope should also have comfortable earpieces. Electronic stethoscopes are available, but their high cost is prohibitive for most veterinary technicians.

Where to listen

During the auscultation, you should be completely focused on the heart sounds. The most important part of the stethoscope is the bit between the earpieces. You should take your time, since rushing will virtually guarantee missing subtle sounds. Your auscultation should be done in a relatively quiet place to ensure background noises do not interfere.

To begin the auscultation, start by palpating the precordium, or the outside of the thorax over the area of the heart. Locate the heartbeat against the chest wall. Known as the apical impulse, it is normally felt on the left hemithorax at about the fifth to sixth intercostal space. Some breed variation in the location of the apical impulse is normal. A stronger apex beat on the right hemithorax is abnormal. If the apex beat is faint or absent, it may be due to obesity or pericardial effusion.

During palpation of the precordium, you should be sensitive to palpable thrills. A thrill is felt when a murmur is so strong that the turbulence associated with the murmur can be felt through the chest wall. The sensation is quite characteristic and feels like a buzzing on your fingers. Take care to distinguish a strong apical impulse from a true thrill.

Now it's time to listen. Cardiac sounds can be divided into two groups: transient sounds and murmurs.