Dog in Heat Symptoms: Swollen Vulva and What Else to Expect

Most dogs in heat feel tired, restless, clingy and physically a bit uncomfortable rather than sick: the swollen vulva, tender nipples, panting and odd appetite are hormone driven, not painful the way an injury is. If your dog seems genuinely unwell during or after a heat cycle, with a fever, vomiting, heavy drinking, or a thick yellow, green or foul smelling discharge, call your veterinarian the same day, because some problems that look like a heat cycle are emergencies. Everything below describes what is typical, what is borderline, and what should move you to the phone.

What is actually happening inside her body

A heat cycle, properly called the oestrous cycle, runs in four stages. In proestrus the ovaries ramp up oestrogen, blood flow to the reproductive tract increases, and the vulva swells and begins to bleed. This is the stage where male dogs are extremely interested and she usually is not. In oestrus, oestrogen falls, progesterone rises, she ovulates, and her behaviour flips: she becomes receptive, flags her tail to the side, and the discharge often lightens. Dioestrus follows whether or not she was bred, with progesterone dominating for weeks. Anoestrus is the quiet stretch between cycles.

Visible signs typically last roughly two to three weeks, and many dogs cycle roughly twice a year, though small breeds often cycle more frequently and large or giant breeds less. A first heat can arrive anywhere from around six months to well past a year of age depending on size and breed.

That hormonal swing is the key to how she feels. Research suggests the behavioural and appetite changes around oestrus are driven largely by the rise and fall of oestrogen and progesterone rather than by pain, which is why a dog in heat can look moody, needy and distracted while her physical exam is completely normal. Results vary from dog to dog: some owners barely notice the cycle, others have a dog who is visibly out of sorts for a fortnight.

The swollen vulva, the discharge and the smell

Vulvar swelling is usually the first thing an owner notices. The tissue becomes firm, enlarged and darker, sometimes two or three times its resting size, and it can look alarming if you have never seen it before. In proestrus it is typically hard and tight; as she moves into oestrus it often softens, which is a useful at home marker that she has become fertile.

Discharge normally starts as bright or dark red blood and becomes more watery, pink or straw coloured as the cycle progresses. Amount varies enormously. Fastidious dogs lick themselves clean constantly and some owners never see a drop, which is why a dog can be well into a cycle before anyone realises. Heavy, persistent bleeding, or bleeding that continues long after the swelling has resolved, is worth a veterinary opinion.

The smell is real and it is hormonal, not hygiene related. Her vaginal secretions and urine carry pheromones that male dogs can detect from a remarkable distance, and many owners describe a distinctly metallic or slightly fishy odour at home. A mild change in smell is normal. A sharp, rotten or pus like odour is not, and neither is a discharge that turns yellow, green or grey. Those belong in the infection section below.

Practical note: she should be kept on lead in public and away from intact males for the entire cycle, including the tail end, because fertility does not switch off neatly on a calendar.

Nipple changes during and after the cycle

Swollen nipples are one of the most searched signs of a dog in heat, and they are normal. Rising oestrogen followed by sustained progesterone causes the mammary tissue to enlarge, so the nipples look puffier, pinker and more prominent, and the surrounding glands may feel slightly firmer. This is more obvious in a dog who has had a litter and in dogs having a later cycle rather than their very first.

The part that catches owners out is the timing. Nipple enlargement often appears or worsens after the bleeding has stopped, because progesterone stays high for weeks in dioestrus whether or not she was mated. That same hormonal pattern can produce a false pregnancy, where a dog nests, carries toys around, goes off her food and develops genuinely enlarged mammary glands, sometimes with milk. It is common, it is not dangerous in itself, and it usually resolves, but a dog producing milk or showing hot, painful, lumpy glands should be examined. Any firm lump in mammary tissue that does not settle once hormones normalise needs a veterinary assessment rather than monitoring at home.

Panting, restlessness and the days she seems tired

Panting during a heat cycle is extremely common and usually reflects hormonal arousal, stress and restlessness rather than heat or pain. Owners describe a dog who paces at night, cannot settle, pants in a cool room, whines at doors, becomes unusually clingy, or alternates between frantic and flat. Some dogs urine mark around the house. Some become irritable with other dogs they normally like. Some shadow their person from room to room for a fortnight.

The flip side is lethargy. A dog in heat can be noticeably tired, sleep more, lose enthusiasm for walks and generally act subdued. Mild, intermittent tiredness that still allows her to get up, greet you, drink and take food is consistent with a normal cycle.

The distinction that matters is depth. Being a bit flat is normal; being unrousable is not. A heat cycle should make your dog seem slightly off, not genuinely ill: a dog who is profoundly lethargic, weak, feverish, vomiting, drinking far more than usual or refusing all food needs to be examined by a veterinarian rather than watched at home. Panting that comes with pale gums, a swollen or tense abdomen, laboured breathing or collapse is an emergency, not a hormone.

What helps in the meantime is low stimulation: shorter lead walks in quiet places, mental enrichment instead of dog park chaos, a predictable routine, a comfortable den space, and washable bedding. Sanitary pants keep the house tidy and stop constant licking, provided they are changed often and she is not left in a damp one.

Appetite loss, picky eating and digestive upset

Appetite changes run in both directions. Many dogs eat less during proestrus and oestrus, pick at meals, or skip one entirely. Others become noticeably hungrier, particularly in dioestrus when progesterone is high. Both patterns are reported and both can be normal. A dog who eats less but still takes treats, drinks normally and holds her weight is usually just distracted and hormonal.

Refusing food completely for more than a day, or losing interest in food alongside vomiting, lethargy or increased thirst, is a different situation and justifies a call.

Digestive upset is also common, especially around a first heat. Soft stools or short lived diarrhoea can accompany the hormonal shift and the stress that goes with it, and some dogs vomit once or twice. Mild, self limiting changes in a dog who is otherwise bright are usually nothing. Diarrhoea that is bloody, black and tarry, profuse, or lasting more than a day, or any gastrointestinal upset in a dog who also seems weak or dehydrated, should be seen. Puppies and small dogs dehydrate quickly, so the threshold for calling should be lower for them. If you are unsure whether what you are seeing crosses that line, talk to your vet rather than waiting it out.

When it is not just heat: signs of infection

The condition every owner should know by name is pyometra, a bacterial infection of the uterus that most often develops in the weeks after a heat cycle in an unspayed dog, when progesterone has thickened the uterine lining and the cervix closes. It is life threatening and it is treated as a surgical emergency. An open pyometra produces a foul, purulent discharge; a closed pyometra produces no discharge at all, which makes it harder to spot and more dangerous. Vaginitis, urinary tract infection and retained post heat discharge can also cause symptoms that overlap with a normal cycle.

Sign	Typical of a normal heat	Warrants a veterinary call
Vulva	Firm, enlarged, softening later in the cycle	Hot, painful, ulcerated, or still swollen long after the cycle
Discharge	Red to pink to straw coloured, mild metallic smell	Yellow, green, grey or pus like, foul or rotten smell
Energy	Slightly flat or restless, still rousable	Weak, collapsing, unrousable, trembling
Thirst	Normal	Drinking and urinating markedly more than usual
Appetite	Reduced or increased, still eating something	Total refusal of food, repeated vomiting
Abdomen	Normal	Distended, tense or painful to touch
Temperature	Normal	Fever, or a subnormal temperature with collapse
Timing	Signs fade over roughly two to three weeks	New illness appearing in the weeks after the cycle ends

Spaying removes the uterus and ovaries and therefore the heat cycle and the pyometra risk, but the timing of that decision depends on breed, size, age, orthopaedic considerations and your own plans, so it is a conversation to have with your veterinarian rather than a default.

Key Takeaways

• A swollen vulva and bloody discharge are the earliest and most reliable signs of a heat cycle, and the swelling usually softens as she becomes fertile.
• Swollen, pinker nipples are normal and often appear after the bleeding stops, because progesterone stays high for weeks afterwards.
• Panting, pacing, clinginess, irritability and tiredness are hormonal, not painful, but they should stay mild.
• Reduced appetite, increased appetite and short lived soft stools are all commonly reported, particularly around a first heat.
• A change in discharge colour or smell, heavy thirst, fever, vomiting, a tense abdomen or profound lethargy are not part of a normal cycle.
• Pyometra most often appears in the weeks after a cycle ends and is an emergency.

A heat cycle is a normal physiological event, not an illness, and most dogs get through it needing nothing more than patience, a quiet routine, secure containment and clean bedding. Your veterinarian owns the diagnosis here: they are the one who can distinguish a hormonal slump from an infection, examine the abdomen, run bloodwork or imaging, and advise on whether and when to spay. If anything about this cycle feels different from her usual pattern, or if your gut says she is unwell rather than simply in season, have her seen.

Related reading: Dog Emergency Signs.