Our hearts beat somewhere around 80 times per minute, every minute, of every day, of every year…until we die. When we are stressed, our hearts beat faster; stronger. When the heart squeezes, we call it systole. Our hearts are incredibly strong and efficient, never really resting. But the faster they beat, the less time they have to fill up between beats, the period we call diastole. When diastole is too short, our hearts remain relatively empty and don’t fill up...