Hydrate well in the days before, then fast for two hours before your appointment (water is fine). Avoid all caffeine for 24 hours and smoking for 12 hours beforehand. Don't do strenuous exercise on the day.

Take your regular medications unless your doctor tells you otherwise. Do not take erectile dysfunction medication in the days before — call us about timing.

Caffeine speeds up your heart and makes the scan harder to interpret. The clearest CTCA images are taken when your heart is beating slowly and steadily, so avoiding caffeine for the full 24 hours before makes a real difference to image quality.

The clearest pictures of the coronary arteries are taken when the heart is moving slowly. If your heart rate is above about 60 to 65 beats per minute when you arrive, we may give you a beta-blocker tablet or injection to slow it gently. This is the main reason your appointment runs longer than the 20-minute scan.

The X-ray scan itself doesn't hurt. You won't feel the X-rays.

When the contrast dye is given, you may notice a brief warm flush spreading through your body and a metallic taste in your mouth. The spray under your tongue may give you a brief headache or feeling of fullness in the head. All of this passes within a minute or two.

The scan itself takes about 20 minutes. Allow 2 to 3 hours at the clinic in total to cover check-in, heart-rate medication (if needed), the scan and a short period of monitoring afterwards.

Yes. CTCA needs a referral from your GP, cardiologist or specialist. Bring the original on the day, or have a photo of it on your phone when you book.

If you've had heart-rate medication, we recommend bringing a driver. Beta-blocker can sometimes cause tiredness or lightheadedness, especially if it's the first time you've taken one. If you haven't needed any medication, you can drive yourself.

A traditional invasive angiogram involves threading a thin catheter into your blood vessels from the wrist or groin. A CTCA produces similar pictures of the coronary arteries without going inside the body, using a CT scanner and a contrast dye given through a vein in your arm.

CTCA is often used as the first investigation. If it shows significant narrowing, a traditional angiogram may still be needed to treat it.

Tell us before your appointment if you're pregnant or think you might be. Your referring doctor and our radiologist will decide whether a CTCA is appropriate, or whether a different test would be more suitable.

CTCA uses more radiation than a plain X-ray. We use low-dose cardiac CT techniques to keep exposure as small as practical while still getting clear images. Your referring doctor will decide whether the diagnostic benefit is appropriate for your situation.