Coughing

Some puppies will cough frequently if they have heart worms. Coughing is often one of the first or only signs of heart worms in puppies. The cough can be mild and is often overlooked as a cold. A coughing puppy should always be taken to a veterinarian, especially if the cough goes from mild to severe and deep chested.

Breathing

Puppies pant a lot because they are very active. If your puppy pants excessively or seems to be gasping for air, seek medical attention. If the puppy is resting but breathing in a labored fashion, it could also be a sign of heart worms.

Exhaustion

All puppies get exhausted after a day of playing and exploring. But beyond normal rest, if the puppies are lethargic, seem to have less energy or appear weak, heart worms may be in the heart already.

Mosquito Bites

Always check puppies for mosquito bites after walks and being outside. Even one bite can be a sign that heart worms have been introduced into the puppy's body and eventually the heart.

Weight Loss

If a puppy is eating well but losing weight or failing to gain, it might be another sign that heart worms are active in the puppy. Puppies with heart worms generally continue to eat and do not vomit as they might with other worms of the digestive tract, but they may not be able to maintain a healthy weight.