ok - God certainly speaks to us in our hearts today. the church affirms this, as does Scripture.
how do you know if it’s God and not your imagination? well, to begin, this presents a bit of a false dichotomy. cs lewis points out in ‘surprised by joy’ the concept of our imaginations being baptized. in other words, sometimes God does indeed speak to us THROUGH our imaginations.
now, the ‘little voice inside’ can tell you all sorts of things. if it disagrees with scripture, the teachings of the church, the wise counsel of a Godly friend, or your conscience, then it’s not God speaking - could be the enemy, could be your flesh, could be the world (you culture and environment, i mean), could be too much pizza last night.
but God has taught me so much right in my heart. He led me to the catholic church that way, among other things. He speaks in a still, small voice, and He speaks constantly. we hear Him best when we have confessed our sins, and it ‘fine tunes’ our hearing to fast. prayer, to a large extent, is listening to that still small voice, as much (or more) as it is talking TO God.
one thing that helps you determine God’s voice from your own (or the enemy’s) is to immerse yourself in Scripture and in the Eucharist. when you learn to recognize ‘His voice’ from scripture, it makes it easier to do so in your heart. the Bible says that His sheep hear His voice. it’s a matter of learning to have sheepish ears.
a final thought on the baptism of the imagination thing - sometimes when i’m at mass, or in eucharistic adoration, or praying the rosary, or just praying, i’ll let my mind wander around. if it gets tied up in something worrisome or sinful, i rope it back in, but let it wander again. very often, God uses this ‘wandering’ to teach me things about my life, and i’ve gotten lots of insights by allowing the shepherd to guide my thoughts to greener pastures.
God bless you as you learn to hear His gentle whispers of love.