Forcast function for ARMA models

I'm trying to use the built-in function forecast. But when I apply it I'm just getting a constant value. Is there any reason for that? or am I just using it wrong? Here is more or less the code:

toEstMdl = arima(2,0,0);
EstMdl = estimate(toEstMdl,Residuals);
estValues = forecast(EstMdl,k);