Monitoring and Guidance of Physical Activity During the Maintenance Phase of Cardiac Rehabilitation: the Antwerp Activity Index

The goal of this clinical trial is to determine whether the AAI activity score can help cardiac rehabilitation patients adhere to physical activity guidelines after participating in an in-hospital cardiac rehabilitation program. The main questions it aims to answer are: 1. Does the AAI activity score have an impact on adherence to physical activity maintenance during phase 3 CR? 2. Does the AAI activity score predict changes in cardiorespiratory fitness? Researchers will compare participants who use the AAI activity score with those who do not to determine if there are differences in physical activity adherence. Participants will: * Wear a smartwatch to continuously measure heart rate for 4 months; * Perform an exercise stress test at the end of the study; * Fill in several questionnaires at the end of the study.