"Angio" means "Blood Vessel". "Gram" or "Graphy" means picture. Therefore, angiogram or angiography means to take a picture of your blood vessels. In this case, the blood vessels of your heart or coronary angiography.
Normal X-ray does not show up any blood vessels. Only when a dye is injected into the vessel can the vessel be seen.
In order to inject the dye into the arteries, a tube or ‘catheter’ has to be placed just outside the arteries of the heart. This tube has to enter your body from the groin or the wrist and follow your body’s artery up to the heart.
The whole procedure may only take 10 minutes to perform. There will be slight pain when some local anaesthetic is injected into the groin or wrist. After which, there will be no more pain.
This is done as a day-surgery. Another words, you will stay on the ward for a few hours after the procedure for observation. You will be discharged on the same day.
You may follow the link to see what an angiogram looks like. The 1st movie shows the left coronary arteries. You may see the tube (Catheter) in the left upper corner. As the dye is injected, you can see the arterial tree come into view.
The 2nd movie shows the right coronary artery. This is a roughly 'C' shaped artery.