Cardiac Auscultation

Cardiac auscultation is a fundamental clinical skill in veterinary practice and remains an important part of assessing cardiac health in small animals. The article explains normal and abnormal heart sounds, murmur classification, and the clinical significance of auscultation findings in dogs and cats.

Normal heart sounds are produced by vibration of cardiac structures and blood flow. The first heart sound (S1) occurs at the start of ventricular contraction and is associated with atrioventricular valve closure. The second heart sound (S2) is caused by closure of the aortic and pulmonic valves. Third and fourth heart sounds (S3 and S4) are usually not audible in small animals and, if present, may indicate severe heart disease with impaired diastolic function.

Effective auscultation involves systematic examination of both sides of the thorax using the diaphragm and bell of the stethoscope. S1 is loudest over the apex beat, while S2 is most audible at the left cranial heart base. The bell of the stethoscope may help detect gallop sounds, particularly in cats.

Heart murmurs are abnormal heart sounds and are classified according to timing, loudness, point of maximal intensity, and radiation. Systolic murmurs occur between S1 and S2 and may be holosystolic or pansystolic. Diastolic murmurs are uncommon in small animals, while continuous murmurs are classically associated with patent ductus arteriosus. Gallop sounds are low-frequency sounds occurring during diastole and may indicate cardiac dysfunction.

Murmur loudness is graded from 1 to 6, although intensity does not always correlate directly with disease severity. Murmurs associated with mitral valve regurgitation are usually loudest over the left hemithorax, while pulmonic and aortic stenosis murmurs are heard best at the left heart base. Tricuspid regurgitation murmurs are typically loudest on the right side.

The paper highlights the challenge of evaluating murmurs in puppies. Innocent murmurs are generally soft, localized, variable, and often disappear by six months of age. Pathological murmurs tend to be louder, radiate widely, and are particularly concerning in predisposed breeds such as Boxers, Golden Retrievers, and Newfoundlands. Puppies with suspected pathological murmurs should undergo echocardiography.

A case example of a Golden Retriever puppy demonstrated moderate subaortic stenosis identified using Doppler echocardiography. Although many dogs with moderate disease tolerate the condition well, affected dogs should not be bred because of hereditary risk.

In cats, auscultation is less reliable for detecting cardiac disease. Many healthy cats may have murmurs, while a significant number of cats with cardiomyopathy may have no audible murmur at all. Additional diagnostic testing, including blood pressure measurement, thyroid testing, biomarkers, and echocardiography, is often required.

The article also discusses dysrhythmias detectable through auscultation. Atrial fibrillation is described as a rapid, chaotic rhythm commonly associated with pulse deficits and structural heart disease. Echocardiography is recommended in these patients to evaluate chamber size and cardiac function.

The paper concludes that accurate auscultation and consistent murmur description are essential clinical skills that support appropriate diagnosis, monitoring, and referral decisions in veterinary cardiology.