OPTImizing CArdiac REhabilitation by REfining Sleep and STress

Inclusion Criteria: * Participate in CR at one of the study centres for any cardiac diagnosis or reason as stated in the Dutch guidelines * Age at or above 18 years * Proficient in the Dutch language * Experiencing sleep and/or stress problems as indicated by a high score on the Pittsburgh Sleep Quality Index (PSQI score \>5) or Perceived Stress Scale-10 (PSS-10 score \>13) * Signed informed consent Exclusion Criteria: * Severe psychiatric, cognitive or physical comorbidity that would impede CR participation * Active treatment for sleep disorders, stress, or other forms of (behavioural) therapy at the start of the study or expected to start within the first 6 months of the study, that could interfere with the RESST intervention. Note: Participants with previously diagnosed sleep disorders are eligible if they still experience sleep or stress problems, unless they fall under the above criteria. Participants who received a prior treatment that is still ongoing but has resulted in a stable sleep and stress condition in the 3 months before the cardiovascular event (e.g., Continuous Positive Airway Pressure (CPAP)) are eligible.