A dog that is still bleeding after four weeks has likely exceeded the normal duration of a heat cycle, and something else may be going on. While some dogs do bleed for up to three weeks during a normal heat, bleeding that persists to the four-week mark warrants a veterinary evaluation. The cause could be as straightforward as a longer-than-average heat cycle or as serious as a uterine infection, ovarian cysts, or a clotting disorder.
What a Normal Heat Cycle Looks Like
Dogs go through two main stages during heat that involve visible bleeding or discharge. The first stage, called proestrus, averages about 9 days and produces the most noticeable bloody discharge. The second stage, estrus, also averages around 9 days, though the discharge typically lightens in color and volume during this phase. Together, the visible signs of heat usually last about two to three weeks.
Here’s the catch: both stages are highly variable. Each one can last anywhere from 3 to 21 days. So in theory, a dog could have a 21-day proestrus followed by a 21-day estrus, putting her at six weeks of discharge. This is uncommon, but it does happen, especially during a dog’s first or second heat cycle when hormonal patterns haven’t fully regulated. If the bleeding has been gradually tapering off in color and amount over four weeks, this may simply be a long but normal cycle. But if the bleeding is heavy, has gotten worse, or is accompanied by other symptoms, the explanation is likely something else entirely.
Ovarian Cysts and Persistent Estrus
One of the more common hormonal explanations for prolonged bleeding is ovarian cysts, specifically follicular cysts. These cysts continuously produce estrogen, which keeps the body locked in a state of heat. Instead of cycling through and moving on, the dog stays in proestrus or estrus indefinitely. This condition is called persistent estrus.
Beyond the prolonged bleeding itself, sustained high estrogen levels create a cascade of other problems. The uterine lining thickens abnormally, raising the risk of a serious uterine infection called pyometra. Over time, excess estrogen can even suppress bone marrow function, reducing the body’s ability to produce blood cells and fight infection. If your dog has been showing signs of heat for more than four weeks with no tapering off, ovarian cysts are a strong possibility your vet will want to investigate with an ultrasound.
Pyometra: A Uterine Infection
Pyometra is a bacterial infection of the uterus that typically develops in the weeks following a heat cycle. In what’s called “open” pyometra, the cervix stays open and the infection drains out as vaginal discharge. This discharge can range from cream-colored to bloody, which is why owners sometimes mistake it for a heat cycle that never ended.
The key differences are context and your dog’s overall condition. Pyometra tends to develop in middle-aged to older unspayed dogs, usually one to two months after heat. Dogs with pyometra often drink more water than usual, urinate more frequently, lose their appetite, or become lethargic. If the cervix is closed and nothing drains out, the situation becomes a life-threatening emergency much faster, but even open pyometra requires prompt treatment. If your dog’s discharge has changed in color, smell, or consistency since her heat started, or if she seems unwell in any way, this is a condition your vet will want to rule out quickly.
Bleeding After Giving Birth
If your dog recently had puppies, four weeks of bleeding points to a condition called subinvolution of placental sites. Normally, the uterus heals and shrinks back to its pre-pregnancy size within a few weeks of delivery. In some dogs, particularly first-time mothers under 2.5 years old, the attachment sites where the placentas connected don’t heal on schedule. This leads to persistent bloody vaginal discharge that can continue for weeks.
An estimated 10 to 20 percent of postpartum dogs experience this to some degree. Most cases are mild and resolve on their own, producing only light spotting. In rarer cases, the bleeding becomes heavy enough to cause dangerous blood loss that requires a transfusion or surgery. If your dog had a litter within the past month or two and is still bleeding, the volume matters. Light spotting that’s gradually decreasing is likely self-limiting. Heavy or worsening bleeding needs immediate attention.
Vaginal Tumors
Tumors in or around the vagina can cause chronic bloody discharge that mimics a prolonged heat cycle. One specific type, called a transmissible venereal tumor (TVT), is passed between dogs through mating or direct genital contact. These tumors have a cauliflower-like appearance, tend to ulcerate easily, and bleed with minimal contact.
The tricky part is that these tumors can grow deep inside the vaginal canal where they aren’t visible during a casual look. For many owners, the first sign is unexplained blood spots on the floor or carpet. Other types of vaginal masses can cause similar bleeding. If your dog’s discharge doesn’t follow any cyclical pattern, doesn’t change in character over time, or is accompanied by visible swelling around the vulva, a tumor is worth investigating. Your vet can check for masses with a physical exam and vaginoscopy.
Clotting Disorders
Some dogs bleed longer than expected not because of a reproductive problem, but because their blood doesn’t clot properly. Von Willebrand disease is the most common inherited bleeding disorder in dogs. It involves a deficiency in a protein needed for normal clot formation, which means any source of bleeding, including a heat cycle, takes much longer to stop.
Type I is the mildest and most common form, seen frequently in Doberman Pinschers, and causes a moderate increase in bleeding risk. Types II and III are rarer but more severe, with Type III involving a complete absence of the clotting protein. Dogs with clotting disorders often have a history of bleeding issues beyond just prolonged heat: slow healing from minor cuts, excessive bleeding after nail trims, or bruising that seems disproportionate to any injury. If this sounds familiar, a blood test can confirm or rule out the condition.
Bleeding in a Spayed Dog
If your dog has been spayed and is now bleeding from the vulva, that’s abnormal by definition. One well-documented cause is ovarian remnant syndrome, which happens when a small piece of ovarian tissue is left behind or regrows a blood supply after a spay surgery. That tissue remains hormonally active and can trigger all the signs of a heat cycle, including bloody discharge, vulvar swelling, and attracting male dogs.
In one review, about 82 percent of dogs with ovarian remnant syndrome showed blood-tinged vulvar discharge, and roughly 59 percent had visible vulvar swelling. These signs can appear months or even years after the original spay. A blood test measuring hormone levels during a suspected “heat” episode can confirm whether functional ovarian tissue is present, and a second surgery can remove it.
Medication Side Effects
Certain hormone-based medications can trigger prolonged bleeding as a side effect. Estrogen-based treatments, sometimes prescribed for urinary incontinence or used to prevent pregnancy after an accidental mating, can cause vulvar swelling and vaginal bleeding. In more serious cases, excess estrogen suppresses bone marrow function, leading to pale gums, loss of appetite, lethargy, nosebleeds, and tiny red spots on the skin from broken blood vessels. If your dog was given any hormonal medication in the weeks before the bleeding started, let your vet know immediately, as the connection may not be obvious.
What Your Vet Will Check
Figuring out why a dog is still bleeding after four weeks involves a systematic process. Your vet will likely start with a physical exam, including a digital vaginal exam to check for masses or structural abnormalities. Vaginal cytology, which involves examining cells from the vaginal lining under a microscope, helps determine whether your dog is still hormonally in heat or whether something else is causing the discharge.
From there, the workup typically includes a complete blood count to check for anemia or signs of infection, a chemistry panel to assess organ function, a urinalysis, and bacterial cultures of the vaginal discharge. An abdominal ultrasound is often the most revealing test, as it can identify ovarian cysts, uterine fluid consistent with pyometra, masses, or retained placental tissue. In some cases, your vet may also test for brucellosis, a bacterial infection that can cause persistent discharge and is transmissible to humans.
The bottom line: four weeks of bleeding sits right at the edge of what could be a long-but-normal heat cycle, but it also overlaps with the timeline for several conditions that need treatment. The character of the discharge, your dog’s age and reproductive history, and whether she’s showing any other symptoms are the details that will help your vet narrow it down.