"Follow your heart." This has the potential to be the worst advice known to mankind. According to the Prophet Jeremiah, our hearts are "desperately wicked" (Jeremiah 17:9). Most of us don't want to believe this, but God's assessment is from perfect knowledge, and our motives and actions pretty much nail us and prove Him right.
We can't follow a heart that is like that! It can get worse...
When we don't recognize God for who He is and worship Him above all things, we lead ourselves into dangerous grounds with our hearts. Notice what happens when a "desperately wicked" heart is given over to its natural course. Notice what following that type heart leads to!
"Therefore God gave them up in the lusts of their hearts to impurity, to the dishonoring of their bodies among themselves, because they exchanged the truth about God for a lie and worshiped and served the creature rather than the Creator, who is blessed forever! Amen." (Romans 1:24-25, ESV)
Before we can follow our hearts, we need a new heart. We need what God spoke of through Prophet Ezekiel, when He said, "And I will give you a new heart, and a new spirit I will put within you. And I will remove the heart of stone from your flesh and give you a heart of flesh" (Ezekiel 36:26). Then, that heart needs constant guarding (Proverbs 4:23) and abiding (John 15). Without the new heart, and without the Spirit's constant help, we will epitomize Ecclesiastes 10:2, which says, "A wise man’s heart inclines him to the right, but a fool’s heart to the left."
New heart; surrendered heart; growing, guarded heart: wise.
Stone heart; heart that follows own desires: fool.
I only trust my heart when it agrees with God. Period.
"Follow your heart" may indeed, depending on the condition of the heart, be the worst advice ever given.