Yes, Nandina is toxic to dogs!
Dogs accidentally consuming the Nandina plants can show the following clinical symptoms: Vomiting, Prolonged Depression, Incoordination, Hypersalivaton, Sleepiness Or Excitation, Dilated Pupils, Low Body Temperature, Low Blood Pressure, Coma, Seizure And Death (In Rare Cases).
Nandina consumption is also toxic to Cats and Horses.
Toxic Principles Of Nandina: Cyanogenic glycosides.
More Info About The Nandina Plant
Scientific Name: Nandina domestica
Family: Berberidaceae.
Also known as: Sacred Bamboo, Heavenly Bamboo.
The answer is based on information found on The American Society for the Prevention of Cruelty to Animals (ASPCA) website.