R code used to produce the graph shown below.

library(isdals) 
data(fev) 
model <- lm(FEV ~ Ht + I(Ht^2) + Gender + Smoke + Age, 
            data=fev) 
corr2 <- cov2cor(vcov(model))     # Correlation matrix 
plotcorr(corr2,  type="lower", diag=TRUE, , col=myblue) 
par(new=TRUE)                     # Keep 1st plot and add numbers 
plotcorr(corr2, type="upper", diag=TRUE, numbers=TRUE, cex=1.6)