Sometimes, the first sign will be fluid feces streaked with blood. Dogs may dehydrate rapidly due to vomiting and diarrhea. Some dogs may vomit repeatedly and have projectile and bloody diarrhea until they die. Others may have loose feces and recover without complications. Most deaths occur within 48-72 hours following the onset of clinical signs.
Pups suffer most with shock-like deaths, occurring as early as two days after the onset of illness.
Now, due to widespread vaccination, these percentages have decreased dramatically. Puppies, between weaning and six months of age are at increased risk of acquiring the disease. This syndrome occurs without concurrent diarrhea because the virus multiplies rapidly in muscle cells of the growing heart. Pups with parvoviral myocarditis may act depressed and stop suckling shortly before they collapse gasping for breath. Death may follow within minutes.