Tapeworms are carried in the stomachs of fleas so when animals ingest them, the tapeworms are free to infest the GI tract. Segments of the worm may break off and be visible in your pets stool (it will look like pasta or grain of rice). Even though most heartworm prevention help prevent intestinal parasites, tapeworms aren't one they cover. It is very important to have pet's stool check every 6 months by your veterinarian. Most intestinal parasites can be identified under microscopic analysis when the parasites are shedding their eggs. Although, most times tapeworms are diagnosed by observation rather than microscopic analysis.