A soft, short duration (beginning of systole) murmur is appreciated in these sounds, graded at 1/6 and loudest at the left heart base.
No structural heart disease is identified in these thin or athletic dogs on echocardiogram. Innocent or physiologic murmurs are often detected in young animals with no evidence of structural cardiac disease, and functional (physiologic) murmurs are usually caused by decreased blood viscosity or increased cardiac tone. Innocent murmurs in puppies should disappear as the dog matures; they are likely the result of larger stroke volumes in puppies (relative to great vessel size) as compared with adults. Physiologic murmurs in boxers, golden retrievers, and greyhounds are not uncommon, particularly in thin dogs in good body condition. Physiologic murmurs can also occur with anemia, fever, hypertension, pregnancy, hyperthyroidism, high sympathetic tone, and hypoproteinemia.