A Single-arm Pilot and Feasibility Study of the CALM Hearts Intervention

Recruitment will be assessed using the following criteria:

• Percentage of WARM Hearts participants who are eligible. Criterion = Observe and report
• Percentage of eligible participants who agree to participate. Criterion = Observe and report
• Average time for enrollment, baseline questionnaire and scheduling. Criterion = 2 weeks
• Most successful recruitment strategy. Criterion = Observe and report

Retention and adherence will be assessed using the following criteria:

• Participant retention rate. Criterion = 80-85% at post-intervention
• Demographics of withdrawn participants. Criterion = Observe and report
• Reasons for withdrawal. Criterion = Observe and report
• Session attendance. Criterion = 90%-95% attendance
• Rates of questionnaire completion. Criterion = 80% overall completion
• Home practice compliance. Criterion = 75% compliance

Fidelity will be assessed using the following criteria:

• Completion of all slides in sessions. Criterion = 90%-95% slide completion
• Completion of topics in sessions. Criterion = 90%-95% topic completion
• Completion of sessions within the allotted time. Criterion = 90%-95% timely completion
• Quality of intervention delivery. Criterion = >80% fidelity as scored by the senior researcher
• Technical difficulties with intervention delivery. Criterion = Observe and report

Capacity will be assessed using the following criteria:

• Time required to deliver all aspects of the intervention. Criterion = Observe and report

Acceptability will be assessed using post-intervention interviews and open-ended surveys administered to participants. Suggestions for increasing acceptability will be noted.

Safety will be assessed using post-intervention interviews and open-ended surveys administered to participants. The criterion for safety = 100% safe.

Self-Compassion Scale (Neff, 2003): Participants responded to 26 questions about their tendency to treat themselves with self-compassion or self-criticism using a five-point Likert scale (1 = almost never to 5 = almost always). A total score of self-compassion was determined by adding the means of all six sub-scales together and dividing by six (Neff, 2003b). Scores from this scale have good test-retest reliability (r = .80-.93) with high internal consistency (α = .92; Neff, 2003b). A sample item includes: "When things are going badly for me, I see the difficulties as part of life that everyone goes through".

Health anxiety subscale of the Multidimensional Health Questionnaire (Snell & Johnson,1997): This scale consists of five items assessing participants' health anxiety on a 5-point Likert scale (1 = not at all characteristic of me to 5 = very characteristic of me). A mean score is created to capture overall health anxiety. The Multidimensional Health Questionnaire is reliable and validated (Snell & Johnson, 1997). A sample item is: "I feel anxious when I think about my health".

Illness self-blame subscale of the Multidimensional Health Questionnaire (Snell & Johnson, 1997): This reliable and validated measure (Snell & Johnson, 1997) uses five items rated on a 5-point Likert scale (1 = not at all characteristic of me to 5 = very characteristic of me) to create a mean illness self-blame score (Snell & Johnson, 1997). A sample item is: "When I become sick or ill, I am the person to blame".

State Rumination Scale (Puterman et al., 2010): Participants responded to three items with a 5-point Likert scale (1= Not at all to 5 = A lot). A mean score was calculated to capture participants' state rumination about having a heart health risk. This scale is reliable and valid (Puterman et al., 2010). A sample item is: "Did you find it hard to stop thinking about your risk for heart disease afterwards?"

Assessment of Negative Affect (Terry et al., 2013): Participants responded to 13 items using a 5-point Likert scale (1=not at all to 5=extremely). A mean score was calculated to assess negative affect about having a heart health risk. This measure has been used in other self-compassion research (Terry et al., 2013). A sample item is: "Rate the extent to which you feel sad about your risk for heart disease".

Health Promoting Lifestyle Profile-II (Walker & Hill-Polerecky, 1996): Participants responded to 52 questions about their engagement in various health-promoting behaviours using a 4-point Likert scale (1 = Never to 4 = Routinely). A mean score was calculated for each subscale, and a grand mean was calculated to assess overall health-promoting behaviours. This scale has demonstrated high internal consistency (Walker & Hill-Polerecky, 1996). Participants were asked to respond to the frequency with which they engage in different behaviours, such as "Choose a diet low in fat, saturated fat, and cholesterol."

Short-form International Physical Activity Questionnaire (Craig et al, 2003): Participants reported the number of days they engaged in each intensity of physical activity and the average duration of each session. This is a reliable and valid measure (Lee et al., 2011). We used the International Physical Activity Questionnaire to calculate participants' weekly minutes of moderate-to-vigorous physical activity. A sample item includes: "During the last 7 days, how many bouts of 10 minutes or more did you complete of vigorous physical activities like heavy lifting, digging, aerobics, or fast bicycling?".