Thatch and I have returned from the vet and we've learned the results of his his echocardiogram: a problem with the muscle controlling the left ventricle of his heart, which is already too thick and will continue to affect his blood flow. He will be on a daily medication for the remainder of his life to slow the heart rate to slow down the muscle's thickening, eventually closing down the ventricle.
I have no idea what this means for his mortality or its longevity, but a part of me died today. I will love him, care for him, and pray to God that he has a long and healthy life.