100%. CPR initiated within 2 minutes of cardiac arrest increases survival rate by 81%. The fact that CPR is rarely initiated so quickly (and thus survival rates are extremely low), says nothing about the efficacy of CPR. In the best cases where CPR is initiated < 2 mins, and AED shock within < 5mins survival rate can be as high as 50%.
https://newsroom.heart.org/news/bystander-cpr-up-to-10-minut...