Yes, Vinca is toxic to dogs!
Dogs accidentally consuming the Vinca 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).
Vinca consumption is also toxic to Cats and Horses.
Toxic Principles Of Vinca: Vinca Alkaloids.
More Info About The Vinca Plant
Scientific Name: Vinca rosea
Family: Apocynaceae.
Also known as: Periwinkle, Running Myrtle.
The answer is based on information found on The American Society for the Prevention of Cruelty to Animals (ASPCA) website.