From the HealthyPet.com Website

• Cardiovascular Toxins
  Avocado (leaves, seeds, stem, skin)*
  Azalea (entire rhododendron family)
  Autumn crocus (Colchicum autumnale)*
  Bleeding heart*
  Castor bean*
  Foxglove (Digitalis)*
  Kalanchoe*
  Lily-of-the-valley*
  Milkweed*
  Mistletoe berries*
  Mountain laurel
  Oleander *
  Rosary Pea*
  Yew*
  
  Gastrointestinal Toxins
  Amaryllis bulb*
  Azalea (entire rhododendron family)
  Autumn crocus (Colchicum autumnale)*
  Bird of Paradise
  Bittersweet
  Boxwood
  Buckeye
  Buttercup (Ranunculus)
  Caffeine
  Castor bean*
  Chocolate *
  Chrysanthemum (a natural source of pyrethrins)
  Clematis
  Crocus bulb
  Croton (Codiaeum sp.)
  Cyclamen bulb
  Dumb cane (Dieffenbachia)*
  English ivy (All Hedera species of ivy)
  Garlic*
  Hyacinth bulbs
  Holly berries
  Iris corms
  Lily (bulbs of most species)
  Marijuana or hemp (Cannabis)*
  Narcissus, daffodil (Narcissus)
  Onions*
  Pencil cactus/plant*
  Potato (leaves and stem)
  Rosary Pea*
  Spurge (Euphorbia sp.)
  Tomatoes (leaves and stem)
  
  Respiratory Toxin
  Almonds*
  Apricot*
  Cherries*
  Chinese sacred or heavenly bamboo*
  Dumb cane (Dieffenbachia)*
  Elderberry, unripe berries*
  Hydrangea*
  Jimson weed*
  Peaches*
  
  Neurological Toxins
  Alcohol (all beverages, ethanol, methanol, isopropyl)
  Amaryllis bulb*
  Azalea (entire rhododendron family)
  Bracken fern
  Buckeye
  Caffeine
  Castor bean*
  Chocolate*
  Choke cherry, unripe berries*
  Chrysanthemum (natural source of pyrethrins)
  Crocus bulb
  Delphinium, larkspur, monkshood*
  Lupine species
  Marijuana or hemp (Cannabis)*
  Mistletoe berries*
  Morning glory*
  Poinsettia
  Potato (leaves and stem)
  Rosary Pea*
  Tomatoes (leaves and stem)
  
  Kidney/Organ Failure Toxins
  Anthurium*
  Begonia*
  Caladium*
  Calla lily*
  Jack-in-the-pulpit*
  Lantana*
  Oak*
  Philodendron*
  Rhubarb leaves*
  Scheffelera*
  Shamrock*
• [*] Extremely toxic and possibly fatal

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