Carbon dioxide is present in the atmosphere (air) at concentration levels of 0.040 % only. So it is non toxic for the human beings and animals.
The human body can adapt to higher levels of concentration of CO2 for some duration, but that is not too long.
If the concentration is increased to 8% or so, then it becomes toxic. people will feel dizzy, suffocated and can faint. It turns poisonous indirectly as the concentration increases.
At its concentration in air, it is non toxic. But pure CO2 is toxic.