Dog in Heat Symptoms That Signal a Problem

If your female dog is in heat (estrus), you can expect some very normal changes: a swollen vulva, a little bloody discharge, and extra clingy or flirty behavior. Many dogs cycle without major issues, but the risk of complications like uterine infection increases with age and with repeated cycles in dogs that are intact (not spayed).

But there are a few heat-related symptoms that are not “just hormones.” Some are true emergencies, and others are early warning signs that deserve a same-day call to your veterinarian.

What is normal during a heat cycle?

Knowing what is typical makes it much easier to spot what is not.

Common normal signs

• Vulvar swelling that develops over days
• Bloody to pink discharge early on, often becoming lighter, watery, or straw-colored as the cycle progresses
• Frequent urination and extra interest from male dogs
• Behavior changes like restlessness, clinginess, “flirting,” or mild irritability
• Decreased appetite for a day or two in some dogs

How long does heat last?

Owners usually notice visible heat signs (swelling and discharge) for about 2 to 3 weeks, sometimes up to 4 weeks. This typically reflects the combined phases of proestrus (earlier bleeding and swelling) plus estrus (standing heat). The full reproductive cycle is longer because it also includes diestrus and a resting phase (anestrus).

Practical fertility note: fertility often rises when discharge becomes lighter and your dog enters standing heat, meaning she may “flag” her tail to the side and stand to be bred. This is one reason strict supervision is important even when bleeding seems to be “ending.”

Heat symptoms that signal a problem

The symptoms below are the ones I want you to take seriously. In a clinic setting, these are exactly the changes that make us move a patient to the front of the line.

1) Heavy bleeding, clots, or bleeding that worsens

Light to moderate spotting can be normal. Bleeding that soaks bedding, drips steadily, seems heavier than typical spotting, contains repeated or large clots, or suddenly increases after improving is not typical and can point to infection, trauma, or other reproductive tract disease.

• Call your vet the same day if bleeding seems heavy or your dog seems weak.
• Go to emergency care if you see pale gums, collapse, or labored breathing.

2) Discharge that is thick, yellow/green, foul-smelling, or pus-like

A normal heat discharge is usually bloody and then becomes lighter or watery. Thick discharge, a bad odor, or pus can suggest infection, and one condition we worry about most is pyometra, a potentially life-threatening uterine infection that can occur in intact females.

Do not wait it out. Pyometra can progress quickly and often needs urgent treatment.

3) Drinking much more water, urinating more, or having accidents

Some increase in urination can be normal because dogs “mark” more while in heat. But marked thirst, very frequent urination, accidents in a previously housetrained dog, or straining can indicate:

• Urinary tract infection
• Diabetes or kidney issues (less common, but important)
• Pyometra (often causes increased thirst and urination)

If these signs show up, schedule a vet visit promptly.

4) Lethargy, weakness, pale gums, or acting “not herself”

Heat can make some dogs restless, but it should not make them profoundly tired, weak, or mentally dull. If your dog seems unwell, trust your instincts.

• Emergency signs: pale or white gums, collapse, difficulty breathing, severe weakness, or repeated vomiting with marked lethargy
• Same-day signs: unusual tiredness, hiding, trembling, refusing food for more than 24 hours

5) Vomiting, diarrhea, or a painful belly

Mild appetite shifts can happen, but vomiting and diarrhea are not “normal heat symptoms” to brush off, especially if you also notice abdominal swelling, sensitivity when picked up, a hunched posture, or obvious belly pain. These can occur with uterine infection or other serious problems.

6) Possible fever plus illness signs

Warm ears are not a reliable way to check for fever. If your dog feels hot and is acting sick (lethargy, shivering, panting at rest, not eating), check a rectal temperature if you can do so safely.

• Typical normal: about 100 to 102.5°F (37.8 to 39.2°C)
• Fever is often: over 103°F (39.4°C)

If you suspect fever, especially with abnormal discharge or a painful belly, this deserves urgent veterinary attention.

7) Heat lasts unusually long or returns too soon

Contact your veterinarian if:

• Bleeding or discharge continues longer than about 3 to 4 weeks
• Your dog appears to go into heat again after only a short break
• You see ongoing vulvar swelling and discharge without the usual pattern

For context, many dogs cycle about every 6 months, but intervals vary widely by breed and individual. Hormonal imbalances, ovarian cysts, and uterine disease can all disrupt normal cycles.

8) New symptoms after heat ends (a big one)

Some of the most dangerous conditions show up weeks after a heat cycle. Watch for:

• Increased thirst and urination
• Lethargy
• Vomiting
• Loss of appetite
• Abdominal enlargement

This timing is classic for pyometra and should be treated as urgent.

Pyometra: a risk intact dog owners should know

Pyometra is an infection of the uterus that most often occurs in middle-aged and older intact females, but it can occur in younger dogs too. It typically develops weeks after heat when the uterus has been hormonally primed.

Common symptoms

• Increased thirst and urination
• Lethargy
• Vomiting
• Fever (not always)
• Loss of appetite
• Vaginal discharge if the cervix is open (there may be no discharge if the cervix is closed)

Why it is urgent: untreated pyometra can lead to sepsis and can be fatal. Treatment often involves emergency spay surgery plus supportive care, depending on the case.

False pregnancy: when nesting is a concern

Some intact females experience a false pregnancy about 6 to 10 weeks after heat due to normal hormone shifts. Mild cases can look like nesting, carrying toys, or mild mammary enlargement.

Call your vet if you notice

• Hard, hot, painful mammary glands
• Milk production with redness, fever, or lethargy (possible mastitis)
• Behavioral distress or aggression that feels unmanageable
• Any sign of illness (vomiting, not eating, weakness)

Your veterinarian can help you decide whether monitoring is enough or if treatment is needed.

What you can do at home

You do not have to guess your way through a heat cycle. A little structure goes a long way.

Practical monitoring tips

• Track dates: first day you notice bleeding, behavior changes, and when discharge stops.
• Check gums once daily: healthy gums are usually pink and moist. Pale gums are a red flag.
• Measure water if you are unsure: a sudden jump in intake is worth a call.
• Take a photo of discharge if it changes: color and thickness matter clinically.
• Prevent pregnancy: keep her away from intact males. Supervise outside, use a leash, and remember that determined males can be surprisingly persistent.

Keeping her comfortable

• Use washable bedding and consider dog heat panties for short, supervised periods only (never leave on unattended). Change them frequently and check the skin for moisture irritation.
• Keep walks calm and leashed.
• Offer normal meals. If appetite dips briefly, focus on hydration and call your vet if she refuses food for more than 24 hours.

When to call the vet vs. go to emergency

Go to an emergency vet now

• Collapse, extreme weakness, or trouble breathing
• Pale or white gums
• Continuous heavy bleeding or signs of shock
• Repeated vomiting, painful belly, or severe lethargy
• Suspected pyometra symptoms, especially in the weeks after heat, with your dog acting ill

Call your vet today

• Foul-smelling, yellow or green, or thick discharge
• Marked increase in thirst and urination
• Heat signs lasting longer than about 3 to 4 weeks
• Straining to urinate, frequent small urinations, or accidents
• Mammary gland pain, heat, or swelling after heat

If your dog is intact and suddenly seems sick during a heat cycle or in the weeks after, treat it like a real medical issue, not a “wait and see” situation.

Quick note: This article is educational and not a substitute for veterinary care. If you are unsure, it is always appropriate to call your clinic and describe what you are seeing.