Today, I will explain to my healthy transplanted heart why, in what may be a matter of days or weeks at best, she — well, we — will die.

I slide my hand across my chest and speak aloud, palm to my heart’s crisp beating. “I’m so sorry, sweet girl.” She is not used to hearing me this way, outside my head, beyond the body we share. Up until now, the understanding between us has been internal. Like on our daily runs, when my ’70s yacht rock playlist propels each stride; this heart from a 13-year-old donor revolts in my body with thumps of Oh puh-lease — and we giggle together, picking up our pace to sprinting.

“She was an athlete,” the doctor told me after a surgeon removed my failing heart (the first transplanted one — yes, I’ve had two) and sewed this second beauty beneath my breastbone. Three weeks later, at my high school track I began the trial-and-error process of figuring out how to defy the uncomfortable staccato of her adrenaline-fueled pulse — a consequence of the permanently severed nerves that cannot regrow to full electrical function inside a recipient’s chest. The idea to run with my new donor heart stemmed from the lessons of my previous one that taught me the importance of mastering maximum heart rate sensations early on.

My 35 years living with two different donor hearts (I was 25 at the time of the first transplant) — finishing law school, getting married, becoming a mother and writing two books — has felt like a quest to outlast a limited life expectancy. With compulsive compliance, I adhered to the strictest interpretation of transplant protocols. I honored my gifts of life with self-discipline: not one pat of butter; not one sip of alcohol; running mile after mile hoping to stave off vasculopathy, an insidious artery disease that often besets transplanted hearts within about 10 years.