The intervention is based on the brief and structured Sources of Meaning Card Method (SoMeCaM; www.somecam.org), which has been adapted for use in groups in a cardiac rehabilitation context. The method uses 26 cards, each representing a specific source of meaning. Approximately 6-10 participants are guided through a process of individually prioritizing the cards, reflecting on them and identifying potential areas for change or development in smaller groups. The group-based format enables mutual sharing and support in reflection and change processes among patients.

The workshop is facilitated by a professional (trained master students in psychology) and followed up with individual phone calls with all participants approximately 4 weeks after the conversation.

The intervention is based on the brief and structured Sources of Meaning Card Method (SoMeCaM; www.somecam.org), which has been adapted for use in dyads in a cardiac rehabilitation context. The method uses 26 cards, each representing a specific source of meaning. The dyadic format considers both the patient's and the relative's individual and shared sources of meaning in 1 session, which may enhance understanding for each other's sources of meaning and facilitate their joint daily life. They both prioritize the cards individually, reflect on them and identify possibilities for change through a talk-and-listen approach.

The conversation is facilitated by a professional (trained master students in psychology) and followed up with a phone call approximately 4 weeks after the conversation.

Changes in participants' self-reported experience of meaning in life will be assessed using two validated subscales from the Sources of Meaning and Meaning in Life Questionnaire: the Meaningfulness and Crisis of Meaning subscales.

Each subscale consists of 5 items, scored on a Likert scale from 0 (Strongly disagree) to 5 (Strongly agree).

For the Meaningfulness subscale, higher scores indicate a stronger sense of meaning in life.

For the Crisis of Meaning subscale, higher scores indicate a stronger experience of life as empty, pointless and lacking of meaning.

Recruitment rate is defined as the proportion of participants who consented to participate in the study, reported as a percentage over the recruitment period.

The proportion of participants who completed the full intervention, defined as participation in the one-session Sources of Meaning conversation (individual, patient-relative, or group-based) and the follow-up phone call. Data will be recorded by the research team.

The proportion of participants who drop out from the study before completing all parts of the intervention, the 3 surveys and focus group and/or individual interview. Dropout will be assessed via administrative data.

Acceptability of the three intervention formats will be explored via focus groups with rehabilitation professionals involved in cardiac rehabilitation. The focus groups will address professionals' views on the interventions and perceived usefulness of the intervention in the municipal cardiac rehabilitation setting.

Defined as the rehabilitation professionals' evaluation of whether the intervention can be successfully used in practice (municipal cardiac rehabilitation). Including factors such as time, resources, and workflow compatibility. Explored via focus group with professionals in the municipal cardiac rehabilitation.

Intervention facilitators will document their experience using semi-structured worksheets with field notes completed after each intervention session. These will capture reflections on feasibility, participant responsiveness, and challenges encountered in each step of the intervention.

Changes in awareness on sources of meaning in everyday life will be explored using a purpose-designed self-report measure with 2 items covering awareness rated on a Likert scale ranging from 0 (Strongly disagree) to 5 (Strongly agree). Higher scores indicate greater awareness on sources of meaning in everyday life.

Changes in engagement in sources of meaning in everyday life will be explored using purpose-designed self-report measure with 3 items covering engagement rated on a Likert scale ranging from 0 (Strongly disagree) to 5 (Strongly agree). Higher scores indicate greater engagement on sources of meaning

Mutual understanding between patients and relatives in the dyadic intervention format will be assessed using the Understanding Subscale of the Perceived Partner Responsiveness Scale (PPRS) (Reis & Carmichael, 2006).

The subscale consists of 5 items rated on a 9-point Likert scale ranging from 1 (Not at all true) to 9 (Very true). Higher scores indicate higher mutual understanding in the relationship to the other person.

Relationship quality will be assessed using the Relationship Ladder, a single-item visual analogue scale in which participants rate their perceived relationship quality on a scale from 0 (Very poor) to 10 (Excellent).

Higher scores indicate better perceived relationship quality.

To calculate intervention costs, information on time spent by intervention facilitators and other staff as well as material costs will be collected.

Reasons for participant dropout will be collected using a voluntary purpose-designed 3-item questionnaire at the time of dropout.

Participant's engagement in the intervention is assessed through 2 purpose-designed questions: (1) 'Thought about the conversation at home' and (2) 'Used the reflection booklet at home'. Each question has an option to elaborate the answer qualitatively.