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Spay the cat. Consider waiting until after the heat is over before spaying. Use hormonal therapy as a last resort.

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Spaying a cat removes her ovaries and prevents the heat cycle from occurring. It prevents her from getting pregnant, and reduces the risk of certain cancers and other diseases.  If you can't afford the surgery, look for low-cost spay services. Many clinics offer this service at a reduced price because it reduces the population of stray cats. Look up your area in the databases listed on the USDA website. There is a small chance of leftover ovarian tissue sending the cat into heat even after the surgery. If this occurs, consult a veterinarian. A vet can perform the spaying procedure at any point in your cat's hormonal cycle — even when she's in heat. However, there's a risk of increased blood loss at that time. The procedure is possible, but consult an experienced veterinarian for advice. The hormones prostaglandin and estrogen can be used to stop a cat’s heat cycle; however, this treatment has serious side effects including uterine infection and tumors. Because of the risks, take this step only when spaying is not an option. Always consult in detail with a vet, who will need to prescribe the hormones and explain how to use them properly. Even if the cat can't be spayed for medical reasons, the risks may not be worth the calm behavior.