CF-Echo Cardiovascular Function: EchoCardiography 11 times
If you haven't been living in a CAVE or anything for the past decade, and caught an episode of... oh, just about any medical drama on television, you've likely seen or heard about "getting an Echo." It's basically ultrasound to take measurements of the heart and blood flow.  

NASA's are slightly cooler than the average bear, since theirs uses three-dimensional imaging.  I've done these tests about 6 times now, and despite being covered with electrodes and gooped up with transducer gunk, it never gets old... I have an endless fascination with watching the ultrasound screen where I can see the live image of my heart beating.  They press buttons and it rotates so they can take freeze-frames of various angles.  Awesome.

PV Plasma Volume Measurement + 100% Oxygen 7 times
Often done in conjunction with other cardiovascular function tests, and used to measure changes in blood.  In micro-gravity, plasma volume is one of the very first things to change internally, and red blood cell mass decreases.  

For this test, we have a thin, flexible catheter tube inserted into an arm vein. They turn off the lights (and their cell phones) for a 20-minute "quiet period" where we are told to keep our hands by our sides, not cross our legs, etc., after which an initial blood sample is taken from the arm.  Through a special apparatus with a snorkel-like mouthpiece, we breathe 100% oxygen from a tank for 1 minute.  A small amount of carbon monoxide (about the equivalent of 2 cigarettes) is piped into the breathing equipment and after 10 further minutes, a second blood sample is drawn for testing.

Vasc Cardiovascular Function + BP after Nitrogylcerin 9 times
The diameter size of our arteries are measured in the upper arm and lower leg with sound waves to get a baseline of what is "normal" for each subject.  After this, a doctor gives us "sublingual nitroglycerin" (places a tiny pill under the tongue), which dissolves in about a minute.  Ultrasound continues on the arm and leg to determine how the large brachial and femoral vessels respond to the nitro, as this medication should cause them to relax/enlarge, and can also cause a drop in blood pressure.  Heart rhythm is watched through the entire process... and in 3 minute intervals, the size of the arteries are measured "3 times per minute."  

I am not actually sure how many times they continue to take readings, because after a few moments, voices and other sounds seem to tune out.  I always get warm, and have a mild feeling of dizziness, like I just want to close my eyes and sleep.  After a few more minutes, however, it feels like someone is crushing your head between a couple of bricks.

The first time I had nitro, I had a monster of a headache for most of the day.  Ditto the second time, only slightly less thunderous.  The third and fourth times?  Nothing.  Symptoms were entirely gone within an hour.  I thought I had grown accustomed to it, or built up a tolerance -- but I guess it can come and go.  This morning was my 5th nitro, and I've spent most of the day feeling like my skull was hit with a hammer.  I have an icepack on my head as I'm typing this... !