Most dogs with a heart tumor live between a few weeks and several months, depending on the type of tumor, how early it’s caught, and whether treatment is pursued. The most common heart tumor in dogs, hemangiosarcoma, carries a median survival of about two to four months with treatment. A less common type called a chemodectoma grows much more slowly and can allow dogs to live well over a year.
Hemangiosarcoma: The Most Common and Most Aggressive
Roughly two-thirds of heart tumors in dogs are hemangiosarcoma, a fast-growing cancer of the blood vessel lining. It tends to form on the right atrium of the heart and spreads quickly to the lungs, liver, and other organs. German Shepherds and Golden Retrievers are the most frequently affected breeds, though any dog can develop it.
The survival numbers for cardiac hemangiosarcoma are sobering. Because the tumor sits on the heart itself, surgery to fully remove it is rarely possible. Treatment typically involves a combination of radiation therapy and chemotherapy rather than surgery alone. With chemotherapy (usually given intravenously every three weeks for five rounds), the median survival time is roughly four to six months. A Brazilian veterinary oncology review found the average survival in treated dogs ranged from 16 days to about 5 months across multiple studies, with chemotherapy extending that to approximately 164 days. Without any treatment, most dogs survive only days to weeks once symptoms appear.
One of the starkest numbers comes from dogs who developed fluid around the heart (a common complication of this tumor): those with hemangiosarcoma had a median survival of just 16 days, compared to over 15 months for dogs whose fluid buildup had a non-cancerous cause.
Chemodectoma: A Slower-Growing Alternative
Chemodectomas (also called aortic body tumors) develop at the base of the heart from specialized tissue that monitors blood oxygen levels. They grow far more slowly than hemangiosarcoma and rarely spread to distant organs. Brachycephalic breeds (short-nosed dogs like Boxers, Bulldogs, and Boston Terriers) are most commonly affected.
Dogs with chemodectomas can live significantly longer. In one multi-institution study, dogs treated with an oral targeted therapy had a median survival of 478 days (about 16 months), with some dogs surviving over two and a half years. Dogs that received additional treatments alongside the oral medication had a median survival of 521 days. Even among the subset with a confirmed tissue diagnosis, survival ranged from roughly 13 to 22 months.
How Staging Affects Survival
Heart tumors are staged from I to III based on how large the tumor is, whether it has ruptured, whether nearby lymph nodes are involved, and whether the cancer has spread to distant organs. Stage I tumors (small, contained, no spread) consistently carry longer survival times than Stage II or III. By the time a heart tumor is diagnosed, though, many dogs are already at an advanced stage because early symptoms are subtle or absent entirely. This makes the stage at diagnosis one of the strongest predictors of how long a dog will live.
Warning Signs That Lead to Diagnosis
Heart tumors often go undetected until they cause fluid to accumulate in the sac surrounding the heart, a condition called pericardial effusion. When that fluid builds up enough, it compresses the heart and prevents it from filling properly. The signs can appear suddenly: weakness, stumbling, collapse, loss of consciousness, cold limbs, pale gums, labored breathing, or a swollen belly. Some dogs show exercise intolerance or an increased breathing rate at rest in the days or weeks before a more dramatic episode.
Dogs with hemangiosarcoma on the heart can collapse or die suddenly if the tumor ruptures, causing fatal bleeding into the chest cavity. This is sometimes the very first sign an owner notices, with no prior warning.
What Treatment Looks Like
For hemangiosarcoma of the heart, direct surgical removal is rarely an option because of the tumor’s location. Instead, veterinary oncologists typically recommend chemotherapy, sometimes combined with radiation. If dangerous fluid has built up around the heart, a veterinarian will drain it with a needle (a procedure called pericardiocentesis) to stabilize the dog before starting cancer treatment. This drainage can provide immediate, dramatic relief, but the fluid often returns.
For chemodectomas, the slow growth rate means some dogs are managed with medication alone. Others may be candidates for surgery depending on exact tumor placement. Because chemodectomas rarely metastasize, treatment focuses on controlling the primary mass and managing any fluid buildup.
In both cases, quality of life is the central consideration. Treatment aims to give dogs comfortable, active time rather than a cure. Most veterinary oncologists will recommend stopping treatment if the side effects begin to outweigh the benefits.
Vaccination Research Showing Longer Survival
One area generating real optimism is cancer vaccination. A phase 2 clinical trial tested an anticancer vaccine alongside standard chemotherapy in 28 dogs with aggressive hemangiosarcoma. For dogs with cardiac hemangiosarcoma specifically, the results were striking: vaccinated dogs had a median survival of 284 days (about 9.5 months) compared to 100 days for dogs receiving only standard treatment. The six-month survival rate was 71.4% for vaccinated dogs versus 0% for those on chemotherapy alone. At one year, 28.6% of vaccinated dogs were still alive.
These are early results from a single trial, and this vaccine is not yet widely available. But for a cancer that typically kills within months, nearly tripling median survival represents a meaningful shift. The vaccine appeared to work by training the immune system to recognize and attack cancer cells, slowing the spread to other organs.
Practical Timeline to Expect
For families trying to plan, here is a realistic summary of the timelines by tumor type:
- Hemangiosarcoma, no treatment: days to a few weeks once symptoms appear
- Hemangiosarcoma, chemotherapy and/or radiation: roughly 2 to 6 months, with a small percentage of dogs exceeding 6 months
- Hemangiosarcoma, chemotherapy plus experimental vaccination: median of about 9.5 months in early trials
- Chemodectoma, with treatment: median of roughly 16 months, with some dogs living over 2 years
Individual dogs can fall well outside these ranges in either direction. A dog diagnosed early with a small, contained tumor and no fluid buildup will generally do better than one presenting in collapse with widespread metastasis. Age, overall health, and how well a dog tolerates treatment all play a role. The numbers above represent medians, meaning half of dogs live longer and half live shorter than those timeframes.