Patent ductus arteriosus is usually diagnosed during a routine physical examination of a young dog showing no overtly abnormal clinical signs. PDA shunts cause a continuous heart murmur that is louder and then softer at identifiable phases of the heart cycle. A skilled veterinarian can detect this murmur when listening to the heart through a stethoscope. This murmur often can be felt by placing the palm of a hand behind the dog’s left elbow; the palpable sensation has been described as feeling like a churning washing machine, giving it the name a “machine murmur.” Dogs with PDAs also can have bounding pulses. Normally, the veterinarian will want to take radiographs (X-rays) of the chest to assess heart, lung and vessel size. An electrocardiogram (ECG) should be conducted to identify any dilation or hypertrophy of the heart chambers and to assess any irregular heart rhythms. Most veterinarians will also recommend evaluating a blood sample to determine whether the dog is anemic.
More advanced testing will involve an ultrasound examination of the heart, which is called an echocardiogram, or simply an “echo.” Advanced tests to confirm a diagnosis of PDA usually are performed by a specialized veterinary cardiologist. An echo can disclose the size of the heart chambers, the thickness of the chamber walls and the degree of contractility of the heart muscle. Special types of echocardiograms can evaluate the speed of blood flow through the patent ductus arteriosus and determine the pressures in the various heart chambers.
It is important to remember that the presence of a heart murmur in a puppy does not necessarily mean that the puppy has heart defects or disease. Many puppies have a low-grade heart murmur early in life that disappears by about 6 months of age. These puppy murmurs are completely normal.