The 2-year-old Chihuahua was barely conscious when his owners found him. His tongue lolled out of his mouth, his pupils were dilated, and his heart beat dangerously slow. When his owners brought him to the emergency clinic in North Carolina, they feared the worst. The 5.5-kilogram dog had collapsed without warning, and his body was struggling to function.

They were very right to be afraid. But what followed was a scientific anomaly.

After emergency treatment and a battery of tests, a toxicology screen revealed what no one expected: the tiny dog had ingested nearly 96 milligrams of cocaine, along with trace amounts of fentanyl. Somehow, he survived. And now, the case—documented in the journal Frontiers in Veterinary Science—is offering new insights into how illicit drugs affect animal hearts in the real world.

“Case reports are crucial in veterinary medicine by providing real-world examples,” said Dr. Jake Johnson, a veterinary cardiology resident at North Carolina State University and lead author of the study. “They capture clinical scenarios that larger studies might miss… ultimately improving emergency preparedness and treatment protocols.”

A Cardiac Puzzle

Cocaine is known to ramp up the body. It typically causes a racing heart, heightened alertness, and, in high doses, dangerous arrhythmias. But when the Chihuahua was hooked up to an electrocardiogram (ECG), the veterinary team saw the opposite.

Instead of speeding up, the dog’s heart was slowing down dramatically. The ECG revealed a first-degree atrioventricular (AV) block, followed by a high-grade second-degree AV block. In simpler terms, the electrical signals that tell the heart when to beat were stalling. His heart rate had plummeted to just 32 beats per minute, around half the minimum for a healthy dog.

Such a reaction is extremely rare in both dogs and humans. Cocaine’s sympathomimetic nature should have sped the heart up, not caused it to falter.

Veterinarians administered a hefty dose of atropine—five times the standard amount—to jump-start the heart. When that didn’t fully correct the rhythm, they followed up with epinephrine. Only then did the Chihuahua’s heart return to a normal pace.

“The net cardiovascular effect of cocaine in canines remains complex,” the authors wrote. “Clinicians should consider cocaine exposure as a possible, though uncommon, cause of high-grade second-degree AV block in canines.”

Dietary Indiscretion

When the dog was transferred to North Carolina State University’s Veterinary Teaching Hospital for monitoring, he was alert and stable. His heart was beating fast again, this time with no irregularities. A focused ultrasound showed a structurally normal heart. Troponin levels, a marker of heart damage, were within range. There was no need for a pacemaker.

But the toxicology report raised more questions than answers. The dog’s urine tested positive not only for cocaine but also for fentanyl and its metabolite norfentanyl. That suggests he may have consumed street cocaine—an increasingly common mixture adulterated with opioids.

The owners denied having any controlled substances at home. They’d recently visited a friend’s house and couldn’t rule out the presence of drugs there. They admitted the dog had a history of “dietary indiscretion”—a polite term for eating whatever he could find.

“Dogs are natural scavengers and will investigate anything on the ground,” said Johnson. “Be vigilant during walks… and use a basket muzzle if necessary.”

The Reality Check

Most veterinary studies on drug toxicity are done under controlled lab conditions, using intravenous administration. But that doesn’t reflect how most pets encounter drugs, which is usually through ingestion or inhalation while nosing around the floor, sidewalk, or trash.

That’s why case reports like this one matter, says Johnson. They bridge the gap between clinical theory and what actually happens in the messiness of everyday life.

Interestingly, this is not the first report of a dog ingesting cocaine. A 2014 study looked at 19 dogs with suspected cocaine toxicosis. Most developed sinus tachycardia—a fast heartbeat. None, however, presented with AV block like this Chihuahua. That makes this the first documented case of its kind.

Researchers suspect that the amount of cocaine—or the route by which it was absorbed—may have played a role in the unusual bradycardia. At high doses, cocaine can act more like a local anesthetic, blocking sodium and potassium channels in the heart. This disrupts the signals that regulate heartbeat.

In humans, high doses have also been linked to AV blocks, though such events are rare. However, in dogs, they’re nearly unheard of outside of laboratory studies.

“Bradyarrhythmias have been linked to cocaine’s inhibitory action on voltage-gated sodium channels within the cardiac myocardium,” the paper notes.

In other words, enough cocaine can turn the heart’s natural rhythm into static.

Lessons for Pet Owners

Despite his near-death experience, the Chihuahua was discharged the next day. He was given no medication, just advice. The owners were told to keep a close eye on him for signs of lethargy, disorientation, or abnormal behavior. They were also told to use a basket muzzle during walks to curb his scavenging.

But the case raises larger concerns.

Drug use in public and private spaces isn’t just a human health risk—it can pose a serious danger to pets. As cocaine and other drugs become more ubiquitous and often adulterated with substances like fentanyl, even a walk in the park could be life-threatening for a curious dog.

Veterinarians urge owners to be honest if they suspect drug exposure. Fear of judgment or legal trouble often delays treatment.

Johnson hopes the case will spur more research into the effects of illicit substances on animals. His work is rooted in the One Health Initiative, a philosophy that sees human, animal, and environmental health as deeply interconnected.

He envisions a future where advanced veterinary care—including things like open-heart surgery and telemedicine—is accessible even in rural clinics. But until then, he says, sharing knowledge through open science and real-world case reports is the best way to save lives—whether human or canine.

“Ultimately, I believe all our knowledge has greater value when it’s passed onto others,” he said. “And research gives me the opportunity to be part of that knowledge-sharing ecosystem.”

For now, the Chihuahua remains a medical mystery with a wagging tail. A reminder that even science’s most confounding cases can have a happy ending.