I must say stethoscope, but this is partly due to my own experience.
About forty years ago, I had a long standing relation with Maria, a very smart and attractive language student, who was very much into medfet.
Every time we were to have sex, she imposed me a complete check up which included taking my rectal temperature on her lap and a lot of stething. She had stolen a brand stethoscope ( Litmann) from her sister who was a MD. As I told Maria I was very afraid of doctors, she said she didnot know anything about cardiology and could not tell if even if I were diing. So I enjoyed those stething session, even more as Maria,.as she guided her stethoscope disc with one hand, used to play with my erect niipples with her over hand. Of course, Maria was never able to perform an ECG on me.
Now, as an old man, I have a minor heart problem and I have been seing several times a year a female cardioogist for about fifteen years. She is now more like a friend to me. Every six months, she does an ECG on me. I would say I don't feel anything during the exam, except the fear that it may reveal a worsening of my condition. On the contrary, when she stethes me, I do feel some kind of erotic excitment as she guides her disc on my chest. On some occasions, I even felt I was developping a real erection and I felt ashamed about it, hoping she did not notice.