Heston Model and antithetic variables

Question

I was implementing some variance reduction techniques for the heston model and came up with a question when implementing the antithetic variable technique. Namely, I was not sure if I had to implement it into the stochastic process (discretized process with the Euler scheme for the underlying and the volatility process) for the underlying and also for the volatility or would it be enough just to implement it in the stock price process?