A rare shock treatment saved a dog from going into cardiac arrest after its heart rate skyrocketed to more than 300 beats per minute.

Six-year-old cockerpoo Elmo's heart rate reached 340 beats per minute, more than double the average heart rate for a dog of his size.

His owners rushed him to the vets in Six Mile Bottom, Cambridge as the longer Elmo was having an abnormal rhythm the more likely he was to have a cardiac arrest.

DWR Veterinary Specialists decided that as Elmo wasn't responding to medication, he should be put under anaesthesia and his heart restarted.

Elmo’s owner, Becky Munting who lives near Halesworth in Suffolk, said: “It was a complete surprise when we first found out what was wrong with Elmo.

He was a very happy, healthy and fit dog and the previous evening had been his normal happy self."

Elmo didn't respond to medication so needed a rare shock treatment to save his life (Image: DWR Veterinary Specialists)
It was suspected the cause of his racing heartbeat was myocarditis, an inflammation of his cardiac muscle, which caused his life-threatening heart rhythm disturbance.

Laurent Locquet, consultant in cardiology at DWR Veterinary Specialists, said, “It is quite rare to have to shock a patient in ventricular tachycardia to go back into a sinus rhythm."

Alice Le Gal, consultant in emergency and critical care, was among the cardiology and emergency critical care team that treated Elmo.

She said: “The longer Elmo was having an abnormal rhythm the more likely he was to have a cardiac arrest.

“We anaesthetised Elmo and gathered a large team for the procedure as there was a risk that Elmo’s heart could stop after the shock and he would require CPR, which we were ready to provide.

“Thankfully after the first shock was applied, Elmo’s heart went back into a much slower more normal rhythm, and he was woken up and continued on anti-arrhythmics in hospital for a few days."

Elmo's owner added: “Elmo is back to his happy, friendly self. Loving life, loving his toys and everyone.

I can’t fault the vets or the nursing team. They looked after Elmo and were always calm and had time to talk things through with us."