Interesting. I have a variation on this "Heart Breathing" that I found very helpful when I needed to relax or sleep. I would meditate upon the name of God while breathing, intoning "Yah" while inhaling, and sounding "Weh" on exhaling. You can say the syllables mentally, rather than aloud, if you wish. If you look it up, you will find the name of God means "the breath as a whirlwind". Life and breathing are intimately related, and the breath whirls like wind down our trachea and bronchi. Think about it. It is a very calming intentional "heart breathing"  life-affirming exercise.