You just paid a few hundred bucks to have your dog "fixed." You endured the "cone of shame," the pathetic whimpering, and the frantic attempts to keep her from jumping on the couch for ten days. Then, six months later, you see it. She’s licking herself constantly. Her vulva looks swollen. To your absolute horror, your neighbor's intact male dog is suddenly howling at your front door like a 1920s crooner.
It feels impossible. You might even think your vet lied to you or skipped a step. But honestly, while it's rare, it happens. Can a dog go in heat after being spayed? Yes. It’s a medical head-scratcher called Ovarian Remnant Syndrome (ORS), and it is exactly as frustrating as it sounds.
Why she’s still acting like she’s in heat
When a female dog is spayed—the technical term is an ovariohysterectomy—the surgeon removes both ovaries and the uterus. No ovaries means no estrogen. No estrogen means no heat cycles. Period.
So, if she's flagging her tail and attracting every male in the zip code, there is estrogen coming from somewhere. Most of the time, a tiny piece of ovarian tissue was accidentally left behind during the surgery. It sounds like a massive blunder, but it’s often more about biology than incompetence. Sometimes, a "supernumerary" ovary exists—basically a third, microscopic bit of ovarian tissue tucked away where it shouldn't be. Other times, a tiny speck of the original ovary breaks off during removal and revascularizes. It finds a blood supply, grafts itself to the abdominal wall or the omentum, and starts pumping out hormones again.
It’s like a zombie organ. It shouldn't be alive, but it is, and it's doing its job perfectly at the worst possible time.
Spotting the signs of a "post-spay" heat
You’ll know it when you see it. The symptoms are identical to a normal heat cycle because, biologically, it is a normal heat cycle.
First, you’ll notice the swelling. The vulva gets significantly larger and firmer. Then comes the discharge. In some dogs, it’s bloody; in others, it’s just straw-colored. Then there’s the behavior. She might become suddenly "flirty," tucking her tail to the side or becoming oddly affectionate with furniture.
Wait. It gets weirder.
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Some dogs don't show physical signs at all but suddenly develop a "phantom pregnancy" a few months later. Their mammary glands swell, they start nesting with socks, and they might even produce milk. This is all driven by the progesterone produced by that stubborn little remnant of tissue. If you see this, don't ignore it. It isn't just a "quirk." It’s a sign that her endocrine system is still fully operational.
The diagnostic headache: Proving she's in heat
You can’t just walk into a clinic and say, "Fix her again." A vet needs proof.
Diagnosis is actually the hardest part of this whole ordeal. If you take her in when she isn't showing symptoms, her hormone levels will look totally normal. To catch the culprit, timing is everything.
Vets usually start with a vaginal cytology. They take a swab of the vaginal wall and look at the cells under a microscope. If they see "cornified" epithelial cells—which look flat and angular—it’s a slam dunk. Those cells only look like that when estrogen is high.
If the cytology is inconclusive, they move to bloodwork. They might test for Resting Progesterone or perform an AMH (Anti-Müllerian Hormone) test. AMH is pretty much the gold standard now. Since AMH is only produced by the ovaries, a positive test in a supposedly spayed dog is a "smoking gun." According to Dr. Jennifer Wardlaw, a board-certified veterinary surgeon, using an hCG or GnRH stimulation test is another way to force that tissue to reveal itself by spiking progesterone levels.
The risk of doing nothing
A lot of owners ask: "Can't I just let her be?"
"She isn't getting pregnant anyway, right?"
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Technically, no, she can't get pregnant if her uterus was removed. But here’s the catch. Leaving that ovarian tissue inside is a ticking time bomb.
Dogs with Ovarian Remnant Syndrome are at a much higher risk for stump pyometra. If even a tiny bit of uterine tissue was left at the "stump" where it was cut, the hormones from the ovarian remnant can cause that stump to become infected and filled with pus. It’s life-threatening.
There’s also the cancer risk. Ovarian remnants are prone to developing tumors because they are often under-vascularized or structurally abnormal. Plus, the constant exposure to estrogen without the balance of a full reproductive cycle increases the risk of mammary tumors. Honestly, it’s safer to go back in and get it out.
The "Second" Surgery: What to expect
If you thought the first spay was stressful, the "re-spay" is a bit more intense. The surgeon has to go on a literal treasure hunt inside your dog's abdomen.
Finding a remnant is like looking for a grain of rice in a bowl of spaghetti. It’s tiny, it’s slippery, and it could be anywhere. Many general practice vets will actually refer you to a board-certified surgeon (DACVS) for this. Why? Because these specialists often use laparoscopy—tiny cameras—to find the tissue without making a massive incision.
Common places surgeons find these remnants include the "ovarian pedicle" (where the ovary originally was) and the "omentum" (the fatty lace that covers the organs). Once it's found and snipped out, the problem is usually solved forever.
Why did this happen to my dog?
It’s easy to blame the vet. Sometimes, it is a surgical error, especially if the dog is deep-chested or very overweight, making visibility difficult. However, ectopic ovarian tissue is a real biological fluke.
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In some cases, the tissue is simply outside the normal anatomical location. This isn't something a vet would see during a standard spay. It’s also worth noting that certain breeds seem to have a higher reported incidence, though the data is still a bit fuzzy on whether that's genetic or just a statistical byproduct of which dogs get spayed most often.
Other things that look like a heat cycle
Before you panic and schedule a second surgery, rule out the "imposters."
- Vaginitis: An infection of the vagina can cause swelling and discharge. It makes the dog lick herself, which mimics heat behavior.
- Estrogen Creams: This is a big one. If you use HRT (Hormone Replacement Therapy) creams on your own skin, and your dog licks your arm or cuddles against you, she can absorb that estrogen. It will cause her to go into a "false heat." This is becoming increasingly common in vet clinics.
- Bladder Infections: Frequent urination and licking can look like heat-related behavior to the untrained eye.
Your immediate checklist
If you suspect your dog is in heat after a spay, don't wait three months to see if it happens again. Document everything.
First, take clear photos of the swelling or discharge. Vets love visual evidence because, by the time you get an appointment, the symptoms might have faded.
Second, check your own medications. Are you using any topical hormones? If yes, stop the dog's access to your skin immediately and see if the symptoms resolve.
Third, ask for a referral to a specialist if your regular vet seems unsure. Ovarian Remnant Syndrome is a niche issue. It requires a specific diagnostic approach.
Lastly, keep her away from intact males. Even if she can’t get pregnant, the "act" of mating can be painful or cause internal injury if she isn't fully healed or if she has a stump infection.
The reality is that can a dog go in heat after being spayed is a question with a "yes" answer that no one wants to hear. It’s a surgical complication, a biological weirdness, and a financial pain. But once that stray tissue is gone, she can finally get back to her hormone-free, "fixed" life, and you can finally stop worrying about the neighborhood dogs serenading your porch.
Actionable steps for owners
- Monitor the calendar: Mark down the exact days you see symptoms. True ORS will usually follow a cyclical pattern (every 6 to 12 months).
- Request an AMH test: It’s the most definitive blood test available for detecting ovarian tissue in spayed females.
- Consult a surgeon: If surgery is required, ask about laparoscopic options to minimize recovery time and increase the chances of finding the remnant.
- Check for "stump" issues: Ensure the vet checks the uterine stump during any exploratory surgery to prevent future pyometra.