What is EASD?

Exercise-Associated Sudden Death (EASD) refers to the unexpected death of a clinically normal horse that occurs during or within one hour of exercise (e.g., during racing, training, cooling down or even bathing post-exercise).

EASD cases are categorized into:

• Diagnosable cases with identifiable postmortem findings, including visible changes in the heart muscle or valves, and pulmonary and other types of hemorrhage.
• Necropsy-negative cases, presumed to be cardiac rhythm problems.

During the first six months of 2025, EASD accounted for approximately 8% of racing fatalities and 18% of training fatalities at racetracks subject to HISA rules (and training centers owned by them).

What HISA is Doing

HISA formed an EASD Working Group in October 2023 and, in August 2024, commissioned two pilot programs to study EASD. In one program, researchers monitored horses in training using Arioneo wearable technology. The lead researchers collaborated with experts worldwide to analyze electrocardiograms (ECGs) in horses actively exercising, which included nine horses that suffered EASD—four of which were wearing devices at the time. HISA also analyzed exercise history data of horses that died in North America to pinpoint potential risk factors.

Resources

Equine Health Advisories

Exercise-Associated Sudden Death (September 25, 2025)

Webinars

How Heart Rhythm Disorders Impact Racehorses: Recognizing What Is Normal and What Is of Concern (October 7, 2025)

Press Releases

HISA Announces New Findings on Exercise-Associated Sudden Death (September 25, 2025)

Exercise-Associated Sudden Death Working Group

Meet the Team