If your procedure is scheduled for the next morning, don't consume anything after midnight. You may have a small breakfast if your procedure is planned for the afternoon. Only drink clear beverages until two hours before your procedure, when you arrive at the hospital. On the morning of your procedure, drink only sips of water while taking your medicines.

Reference:

1. Cardiac catheterization. (n.d.). Retrieved from https://www.mountsinai.org/health-library/tests/cardiac-catheterization