Can a Spayed Pet Still Be in Heat?

Dog with cone sleeping on floor
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It is possible for a female dog or cat that has gone through spay surgery to show signs of heat—bleeding, attracting males, and behavioral changes—after the surgery. Typically, the animal is spayed by the age of 4 months, because both dogs and cats enter their first heat at 4 to 6 months old. If your pet appears to go into heat after the surgery, contact your vet. Most likely some ovarian tissue was left in the body during surgery and that tissue releases hormones that cause the animal to go into heat.

You need to understand female dog and cat anatomy and the spay surgical procedure to understand how a pet can seem to be in heat after a surgery to prevent pregnancy and heat cycles.

About Pet Uterus and Ovaries

In dogs and cats, the uterus is shaped like a long "Y." The body of the uterus is the stem of the Y, which is short relative to the long arms called the horns. The horns are where the puppies and kittens are formed, attached, and grow during gestation.

The ovaries, while separate from the uterus, are attached by way of ligaments and blood vessels to both the uterine horns and body. The veterinarian must separate the ovaries from the attachments in the body by clamping and tying off the blood vessels.

The uterus is then removed at the base of the Y, usually above the cervix so that the cervix remains in the body.

Each ovary is in a sac. The sac is often filled with fat—more so in older or overweight animals. Sometimes, the ovarian tissue is diffuse, sometimes it is small or not well formed at the time of the spay. It may also be ectopic, meaning it isn't where it should be in the body, which is a congenital problem.

What Happens During Surgery

Sometimes, when the veterinarian clamps the tissue to ligate the blood vessels, small bits of ovarian tissue remain in the body after the surgery. This tissue can then grow and respond to chemical signals from the brain to produce the hormones that cause the heat cycle.

How then can the pet actually bleed if the uterus and ovaries have been removed? The lining tissue of the remaining vagina can swell and bleed in response to the hormones, simulating a heat cycle. Unless the uterus was not removed, your pet cannot become pregnant.

Visit the Vet

Other possible situations could simulate a heat cycle. Your pet may have a vaginal or bladder infection. Take your pet to its veterinarian for an examination to find out exactly what is causing your pet's behavior.

Myths About Spayed Pets

  • Despite what you may have heard, it isn't necessary for your pet to go through one heat cycle or have a litter before she is spayed. 
  • Spaying does not cause a pet to be fat or lazy. Overweight dogs are fed too much and receive too little exercise.