Heart Failure in Dogs: Back Leg Weakness and Collapse

Coughing, difficulty breathing, and tiring quickly during exercise are the most common signs of left-sided congestive heart failure.¹ Start with our guide to a senior dog whose back legs are failing, then read on for the cardiac side.

Dog heart failure back legs symptoms worth knowing

• Brief collapse. Syncope, or fainting, is a temporary loss of consciousness that happens when the brain does not get enough oxygen.² An episode starts suddenly with no warning, often during activity; the dog may look weak or wobbly for a moment, then goes limp.² Fainting is more common in older dogs.²
• Tiring easily after activity. Many dogs with congestive heart failure tire out more easily, have reduced stamina, and do not play or walk as they once did.³
• Muscle wasting. Dogs develop generalized weight loss and muscle wasting because of the effects of heart failure on other body systems.³
• A heavy belly. Right-sided congestive heart failure can cause fluid to build up in the abdomen, the chest cavity, liver, and the limbs.¹

What congestive heart failure actually is

Congestive heart failure means the heart cannot pump enough blood for the body.³ Leaky mitral valves alone are estimated to cause about 80% of cases.³ Degenerative valve disease, a thickening of the heart valves, is the most common heart disease in dogs and is more common in older, small-breed dogs.⁴ Dilated cardiomyopathy is the second most common heart disease in dogs and the most common in certain large breeds.⁵

Left-sided failure brings the coughing and breathing signs above, and it is the most common form.³

How it progresses and what owners notice

Degenerative valve disease causes no visible signs in its early stages even though a vet can already hear a murmur, and dilated cardiomyopathy likewise has a very long silent phase before signs appear.⁴ Reassuringly, only about 30% of dogs with a leaking mitral valve go on to develop heart failure.⁴ With proper treatment, many dogs can live a normal life for many months to years.³ We cover timelines in more detail in our piece on what to expect from heart failure in an older dog.

Fainting, seizure or true leg weakness?

Videos of your dog's episodes can be very useful in telling seizures and fainting apart.⁶ Note the gums, the breathing and how long recovery takes.

• Fainting: the episode ends within seconds to minutes and the dog recovers rapidly, with no confused period afterwards.⁶
• Seizure: the legs stiffen then make rhythmic paddling motions, and dogs often chew, vocalise or drool heavily,⁶ and are typically confused and disoriented afterwards.⁶

Red flags that mean go now

Open-mouth or laboured breathing, repeated fainting, a hard swollen belly, or a collapse that does not resolve in a minute or two all need same-day emergency care. Pale or bluish gums, an increased resting breathing rate, a swollen belly or loss of appetite in a dog with a heart murmur should be reported to your veterinarian immediately.³ Sudden paralysis of the back legs can also be a sign of heart trouble: hypertrophic cardiomyopathy, a thickening of the heart muscle seen rarely in small dogs, can lead to the formation of blood clots, with collapse and paralysis of the back legs among the signs.⁴ See our guide on a dog who suddenly cannot walk.

How your vet works it out

Listening with a stethoscope is the first step, and a murmur's location and loudness help determine its significance.³ From there, chest X-rays assess heart size and look for fluid in the lungs,³ an echocardiogram uses ultrasound to evaluate the heart,³ and blood and urine tests check for other disorders.³ Your veterinarian may also recommend referral to a cardiologist or neurologist.² At home, your vet may ask you to count your dog's resting respiratory rate, the breaths taken while sleeping or resting quietly, so changes can be spotted early.³

Movement and support when the heart and the legs are both struggling

Keep movement short, flat, cool and frequent rather than long. Limited exercise is generally suggested for most heart conditions, with the goal of preventing the heart from becoming overburdened,⁵ and dogs whose hearts are pumping less blood may need to decrease their activity level.² Put rugs or runners over slick floors, keep nails short, avoid midday heat and stairs, and use a towel or padded sling under the hips for help up and outside. Ask your vet to set the activity ceiling in minutes, so you both know what "enough" looks like.

Where a rear support wheelchair fits a cardiac dog

The OldPal Rear Support Dog Wheelchair carries weight through the hips and chest with a padded harness rather than the spine, the frame sits so the back legs hang free or lightly brush the ground, and dogs can squat and toilet while in it.

For a dog with a heart condition, use it in short supervised sessions on flat ground, watch the breathing rate during and after, and stop before your dog tires. If breathing is laboured, if the belly is distended, or if your dog is fainting, park the chair and call your vet first.

Sizing uses one measurement: rear leg height from the top of the hip straight down to the toe pad, measured lying on the side with the leg at its natural bend. Five sizes cover 3 to 27 inches. Use the fit finder and measuring guide, or send a photo and your measurement to help@oldpalpets.com and a person will check it.

What to track at home

Keep one simple log: sleeping breaths per minute, weight, belly girth, appetite, and how far your dog walks before the back end fades. Note the date of any collapse and whether it happened during activity. That page of notes, plus a video, is the most useful thing you can hand your vet.

Frequently asked questions

Related guides

• Caring for a dog with weak back legs
• Arthritis in a dog's back legs
• When a dog's back legs keep giving out

Sources