Not all mildly affected dogs have heart murmurs. (rmvccolorado.com)
That's because, while dogs almost always have a loud heart murmur (i.e., one we can hear with our stethoscope) indicative of heart disease, cats often don't have a heart murmur present. (pethealthnetwork.com)
He does have a heart murmur but it does not appear to slow him down or hinder him. (healthypawsla.com)