Many ways exist to correlate the human heart and an aircraft’s powerplant. For example- neither humans nor aircraft survive long with unhealthy powerplants. Similarly- both benefit from regular- hearty exercise. But even after living a healthy life- they can- over time- develop problems that need correction. Surgeons can even make repairs to heart valves and muscle to restore lost utility- much as a good technician can rebuild an engine to bring it back to better health.