I had one about a year ago. I was quite nervous too. There is a lot of conflicting data in these answers here I see. They will give you a little something to relax. It will not put you to sleep, just relax you a little. The area they go into, in your groin will need to be shaved of hair, they usually do both side just in case the doctor has difficulty going in 1 side has to use the other one. They will scrub the area with disinfectant just before. The small, small catheter they place is into the femoral artery in your groin (usually, it can also be put into the brachial artery in your arm). There is pressure but not a lot of pain with insertion of the catheter, they also use a local anesthetic at the site. When they place the dye in through the catheter you will feel a warm flushed feeling throughout your body. It s really strange but they warn you when it s coming. They dye shows up on xray so they can see the vessels of your heart and the chambers. They can evaluate for any blockages in arteries you may have. Afterward they place direct hand pressure to the area for 10 or 15 min to stop any bleeding. It is really important to lie still or however they tell you to lie afterwards. The catheter is put into a large artery which if started bleeding can be dangerous, sometimes the bleeding could happen just inside at the site where they went in, we call this a hematoma, if it gets too big they may have to drain it. I m just telling you the POSSIBLE complications. Depending on what they find and what they do to correct anything they find you may stay only 2 hours after like I did or as long as overnight if they cleaned out they inside of a vessel or placed a stent in a vessel to allow for better blood flow. If you stay 6 hours or overnight you will have restriction on activity. I had a small reaction to the dye, which is also common. I just had a few hives but they gave me Benadryl and I was fine. If you are allergic to Iodine or shellfish it is very important to tell them before hand, they will need to give you medications so there is no reaction or they may not be able to do it. I went home after 2 hours and had to lie down for they rest of day, they really don t want any undue stress to the area, even sitting. I had to take 3 days off work because I am a nurse and they didn t want any heavy lifting or moving heavy objects ( I lift move heavy patients every day). You may be different. The first 2 days the spot they went in did not hurt at all, for the next 3 or 4 it hurt a little and there was a little bruise. It is very important to follow all aftercare instructions they give you and to notify them if there is bledding, redness, discharge, or if you develop fever. It could be s sign of an infection at the site. It is alos important to drink extra fluids after the test to help wash the dye out of your system. Overall, it was no big deal but every one is different and every hospital doctor is different in thier practice with such tests. Good Luck I hope that helped.