“A happy heart makes the face cheerful, but heartache crushes the spirit” (Proverbs 15:13 NIV2011). In this verse we can see that the heart affects our face–KJV says countenance. We have heard the expression “a broken heart” here called heartache. Sounds to me like the happy heart is best, but life can deal some severe blows, which can lead to a broken heart. Grief over the loss of someone close might well lead to that heartache.
I think Solomon isn’t saying we should always have a happy heart, but that what’s in our heart shows up on our face. In other words, the status of our heart, whether happy or sad, affects more than just our heart. It affects the whole, body, soul, and spirit. When Nehemiah went before the king, he asked Nehemiah, “Why does your face look so sad when you are not ill? This can be nothing but sadness of heart.” (Nehemiah 2:2 NIV2011). Nehemiah’s sadness over the condition of Israel showed in his face. Be happy heart.