He is our shepherd, calling us to follow him, so when you hear his voice, obey it. That's what the psalmist is saying. And just like physical heart disease, we need to listen to what God says about our hearts in a spiritual sense. We need to hear his word and act today. Today - means now and it means continually.
Arteriosclerosis is a hardening of the arteries that leads to heart attacks.
And it is possible for us to develop spiritual arteriosclerosis. We can harden our hearts. By not accepting what God says about himself. Modifying His Word. By only accepting the bits we like, for example God's love, and rejecting the bits we don't like, such as God's anger at sin.