Conditions or ailments that are the cause of a problem that you see - your observation.

Your vet may diagnose

Poisoning by Cardiotoxic Plants, Generally

Synonyms: Plant Toxicities Affecting the Heart & Cardiovascular System


A variety of plants of different families contain toxins that directly or indirectly affect the heart. Cardiotoxic plants cause severe acute illness and sudden death in the horse. Horses are usually poisoned when they are given access to ornamental shrubs and lawn clippings.

Lily of the Valley, Oleander, Hellebores, Laurel, Azalea, Rhododendron, Foxglove, Death Camas and Hemp Dogbane all contain cardiac glycosides, which can cause signs similar to heart attack. Certain types of Milkweed contain cardenolides that cause cardiac arrest. English, Canadian and Japanese Yew contain toxic alkaloids (taxine) that inhibit proper heart function. Avocado leaves, fruit and bark is poisonous to horses, as it contains the cardiac toxin persin.

Signs of poisoning by these plants include (among many others) colic, high heart rate, irregular heart beat, sweating, trembling, diarrhea, labored breathing and sudden death.

Usually these horses are found dead, with evidence that they consumed the plant yielding the diagnosis. The glycosides may be found in blood or tissue of properly submitted samples.

There is no known treatment for these poisons.

my role


I might observe

You might make these observations when a horse has this condition.

Very Common
Less Common
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Questions To Ask Your Vet:
  • How can I manage my horses to minimize exposure to these toxins?

Horses should never eat lawn clippings. Remove these plants from areas where horses have access. Particularly keep in mind that horses may reach over a fence to browse green leaves. Hay should be inspected for weeds. Note, many weeds retain their toxicity even when dried.

Know your pasture. Research the plants that grow in and around all of the areas that your horses live. Ensure that you avoid planting toxic plants when landscaping around your barn. Never let a horse eat any plant that you cannot identify and know is harmless. When in doubt, take a picture of the plant and send it to your vet or a botanist for a discussion.

Author: Doug Thal DVM Dipl. ABVP