The investigators will recruit patients from MGH and Brigham and Women's Hospital (BWH) inpatient units who are admitted with a primary cardiac diagnosis of ACS. Following the completion of baseline outcome measures, participants will be randomized to one of eight treatment conditions. All participants will complete PP exercises at least weekly and will speak with a study trainer weekly for eight weeks. Those receiving the PP-only intervention (conditions 1, 2, 5, 6) will speak to a study trainer for 30 minutes each week. Participants in Conditions 3, 4, 7, and 8 will be enrolled in a combined PP plus motivational interviewing (MI)/goal setting program. Accordingly, their weekly phone sessions will focus on the PP program for 15 minutes, then the MI/goal setting program for an additional 15 minutes. These calls will be recorded, and a percentage of calls will be reviewed to ensure that the PP and MI/goal setting portions of the intervention are being delivered as described in the protocol and trainer manual. Half of the participants (conditions 1, 3, 5, 7) will be instructed to perform the PP exercises once per week while the other half (conditions 2, 4, 6, 8) will be asked to perform them once daily. Finally, half of the participants (those in conditions 5-8) will receive three additional 'booster' phone sessions during weeks 10, 12, and 14. These sessions will focus on integrating PP-related skills into daily life. For participants in the PP+MI condition, booster sessions also will focus on maintaining the health behavior changes that they made during the main portion of the study.