Physical Examination of the Cardiovascular System

Heart sounds are produced by valve movements and the resultant vibrations in the heart, vascular walls, and blood columns. In the normal dog and cat, heart sounds that are typically audible include S 1 (“lub”) and S 2 (“dub”) (Fig 1). S 1 , which is associated with closure of the atrioventricular (mitral and tricuspid) valves, is louder, longer, and of lower pitch than S 2 , and is best heard over the those valve regions (M and T) indicated in Figures 2 and 3. S 1 becomes louder with exercise, excitement, or anemia and varies with heart rate and PR interval. The intensity of S 1 also varies with atrial fibrillation, atrial or ventricular premature beats, or marked sinus arrhythmia. S 2 coincides with semilunar (aortic and pulmonic) valve closure and is best heard over the valve locations (A and P) indicated in Figure 2. The intensity of S 2 may increase with pulmonic stenosis, heartworm disease, hyperthyroidism, or pulmonary or systemic hypertension. The intensity is decreased in cardiogenic shock. In normal dogs and cats, S 3 (produced by vibrations associated with rapid ventricular filling) and S 4 (produced by atrial systole) are not audible (Fig 1). These sounds, termed cardiac gallops, are however, detectable in certain disease states.

Abnormal heart sounds offer the veterinarian an indication of the presence of cardiac disease, as well as specific information as to the underlying diagnosis. In some, but not all, instances, abnormal heart sounds give some indication of the severity of the underlying lesion. Careful auscultation, along with information obtained from the remainder of the physical examination, history, and ancillary diagnostic procedures, provides the means by which a specific diagnosis of cardiac disease is made. It should be kept in mind that, in some instances (e.g., anemia), abnormal cardiac sounds do not represent organic heart disease.

Ideally, auscultation of the heart should be performed in a quiet room, with a standing, cooperative patient. Usually the more dramatic heart sounds are evaluated after listening to the more subtle respiratory sounds. A stethoscope is placed over each heart valve (Fig 2) in turn, as well as over the carotid arteries and other areas of interest. The stethoscope’s diaphragm is pressed firmly to the thorax to maximize high frequency sounds, while the bell portion is lightly applied, maximizing low frequency sounds such as cardiac gallops.  […]