I had a benign irregular heartbeat (Premature Ventricular Contractions) for half my life. During one checkup the cardiologist said my heart had become enlarged to compensate, and if I wanted an energy boost I should get an ablation surgery.
The ablation was quite the experience as I was kept conscious throughout (and I felt euphoric thanks to the painkillers). A team of students carefully threaded a wire in through my femoral artery, guided it up to the inside of the heart and zapped the problematic cells. I could actually feel the moment they fixed it. One moment my rhythm was irregular, the next it was regular. They then ran a series of stress tests that included injecting me with something that pushed my heart rate above 200 bpm. That was uncomfortable. I was back to my normal routine 24 hours later and I did indeed have more energy.