Atrial septal defect and persistence of an open foramen ovale are relatively common congenital defects of calves.  These defects provide direct openings between the left and right atrium.  A patent foramen ovale is often partially covered by a membrane.  The underlying etiology for both conditions is unknown.  Patent foramen ovale is accompanied by a patent ductus arteriosis in up to 50% of the affected calves.  The murmur is usually a holosystolic ejection murmur heard loudest over the left heart base.  Because the atrial pressure gradient is low, the murmur is not caused by flow of blood from the left to the right atria.   Rather, it is due to a relative pulmonic stenosis caused by the volume overload through the right side of the heart.

Click on the four primary cardiac auscultation sites to hear their accompanying sounds and answer the following three questions?

Atrial fibrillation is a relatively common dysrhythmia in cattle.  It is most commonly encountered secondary to gastrointestinal disease.  Occasionally it is observed secondary to painful conditions including severe lameness.  In cattle it is readily diagnosed during auscultation due to the extreme irregularity of the heart beat.   Other dysrhythmias that may be confused with atrial fibrillation during auscultation in cattle are sinus arrhythmia and premature atrial contractions.  Clinical impression may sometimes distinguish these however an electrocardiogram is the only way to definitively diagnose the dysrhythmia.

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