The investigators will recruit 60 participants from three cardiac rehabilitation (CR) sites: Liverpool Heart and Chest NHS Foundation Trust (n=20), University Hospitals Coventry and Warwickshire NHS Trust (n=20) and North Tees and Hartlepool Foundation Trust (n=20). The participant information sheet will be added to hospital discharge packs, participants will then be contacted by the CR team immediately post-discharge as part of routine care (within 48h at our named sites). During this contact the CR team will discuss the study information. The research fellow will then contact interested participants and consent and screening will occur via video call. Written informed consent will be captured using the eSignature solution HELLOSIGN, in line with Health Regulation Authority advice.

This is a feasibility, assessor-blind, parallel group randomized control trial (RCT). Participants will be randomized and allocated to either CR standard care (control group) or exercise counselling with mHealth + CR standard care (experimental group). Assessments will be completed twice; 1) immediately post hospital discharge, before any intervention, and 2) after CR. To minimize participant burden and ensure timely completion, outcome measures will be undertaken remotely. Participants will be mailed (guaranteed next day delivery by midday) all necessary assessment resources immediately following consent. Written and video guidance on how to complete the assessments will be provided along with online support from the research fellow.

Participants will be randomised into one of two groups:

1. CR standard care control group: Participants will follow CR standard care and have contact (e.g. telephone/virtual and/or home visit) with the CR team between discharge and beginning CR. Participants will begin structured exercise at the time provided by the CR service, the structured exercise service consists of 1-2 supervised exercise sessions per week for 12 weeks at the clinical or community centre. Exercise sessions are circuit-based, cardiovascular and strength exercise of light to moderate intensity (40-70% heart rate reserve). Participants can wear an unblinded HR monitor during structured exercise provided by the CR service. As part of the study, they will also always wear a blinded optical HR monitor. Patients can keep this kit if you wish or return it to us using a pre-paid envelope. This monitor provides no feedback to participants but provides exercise intensity and adherence data to the research team remotely. Thus, participants will wear 2 watches during CR sessions to receive feedback on HR as would be the case during standard CR, but only 1 blinded watch outside CR, wear during incidental exercise/PA, as part of the study.
2. Exercise counselling with mHealth +CR standard care experimental group: Participants will co-design a personalised and progressive home-based walking program, with support from the research fellow, that starts immediately following hospital discharge and continues as an adjunct once structured exercise CR begins. Each participant's exercise program will differ, but the aim will be to increase exercise intensity and duration throughout the programme with the goal of achieving 150-minutes of moderate intensity exercise per week, when combined with structured exercise CR sessions. To assist with the transition to independent exercise and to promote long-term adherence, participants will receive 4 virtual exercise counselling sessions. The first, held within 5 days of discharge, will be used to assess current beliefs/concerns, explore the benefits of exercise and agree on a SMART (specific, measurable, achievable, relevant and time-bound) PA plan. During this initial phase, participants will be prescribed an individualised (initial duration and intensity of sessions and rate of progression) walking plan. Once structured exercise CR has begun, a second session will be held to discuss progress and refine goals with the aim of progressing the programme. At this time, home-based sessions will be performed alongside structured exercise CR sessions to increase adherence in daily life. A third meeting will be held 1 month into CR to discuss progress. A final meeting will occur at the end of CR to review progress and strategies to maintain exercise and PA. The mHealth technology supported PA and counselling intervention, MOTIVATE, is informed by social cognitive theory. An analysis of the intervention components show MOTIVATE sessions have an emphasis on behaviour change technique categories, including "Goals and Planning," and "Feedback and Monitoring" and motivational interviewing technique processes, including "Engaging" and "Evoking" designed to promote long-term adherence to PA and exercise.

The experimental intervention will be supported by 3 mHealth elements: 1. Online coaching platform for the research fellow. Within the platform the research fellow will build the co-designed exercise programme, specifying the agreed number of sessions per week. Individual exercise sessions will be built, prescribing the duration and intensity (measured through HR) of each phase i.e., warm up, workout and cool-down. Structured exercise CR sessions will also be inserted, when CR begins, so these can be tracked. These detailed exercise sessions will then be available as pre-set sessions on the fitness tracker. Throughout the intervention the online platform will also provide the research fellow access to the participant data including; daily PA, HR during exercise, rate of perceived exertion RPE (CR-10 scale) following exercise sessions and written comments on exercise sessions. 2. Smart phone app for participants (Polar Flow). Participants will access their exercise programme and track exercise and PA achievements and provide feedback on each exercise session; including a session RPE and a written comment. 3. Wrist worn fitness tracker for participants (Polar Ignite, Polar Electro). Will act like a CR specialist on participants' wrists. The Polar Ignite fitness watch features a triaxial accelerometer and optical HR monitor. Patients can keep this kit. Participants will access pre-set exercise sessions, designed by the research fellow, on the device. The prescribed duration and intensity, via HR zones, will be displayed in real time on the watch throughout the exercise session. The watch will also provide live visual and haptic (vibration) alerts, coaching participants to execute the session as prescribed. Progress towards a personalised daily PA target will also be displayed throughout the day on the watch screen. Data from the mHealth elements, including participant comments, will be used to facilitate ongoing personalised feedback. Immediately following hospital discharge and for the 1st month of walking intervention, participants will receive text messages from the research fellow after each exercise session. For the remainder of the walking intervention (including during CR), messages will be sent weekly. Participants will be able to respond to these comments and programmes will be updated if necessary.