Internet-based Behavioral Intervention Following ACS

Inclusion Criteria: * ACS ≥ 6 months before assessment (type 1 MI STEMI/NSTEMI or unstable angina \[UA\]) * Age 18 and older * Clinically significant cardiac anxiety that leads to distress and/or interferes with daily life (Cardiac Anxiety Questionnaire; CAQ: ≥18 * Able to read and write in Swedish Exclusion Criteria: * Heart failure New York heart Association class IV or ejection fraction ≤ 30% * Significant valvular disease * Planned coronary artery bypass surgery or percutaneous interventions * Any medical restriction to physical exercise * Severe medical illness or an acute health threatening disease (e.g., cancer) * Grade 3 hypertension (i.e., blood pressure ≥ 180 systolic and/or 110 diastolic) * Severe mental illness requiring urgent psychiatric hospitalization or intervention, or risk of suicide * Alcohol or substance use disorder that would impede ability to complete study protocol * Ongoing psychological treatment