This exploratory pilot randomized controlled trial evaluates whether a HeartMate application-based remote patient monitoring (RPM) and digital cardiac rehabilitation program improves cardiovascular, functional, and psychological outcomes in patients with cardiac disease. A total of 200 participants with cardiovascluar disease requiring rehabilitation are randomly assigned in a 1:1 ratio to an intervention group or a control group. The intervention group uses the HeartMate app-based remote cardiac rehabilitation program for 6 weeks, including a daily heart check using smartphone remote photoplethysmography (rPPG), aerobic and resistance exercise, breathing training, and a cognitive-behavioral 'mind' program, with weekly remote coaching. The control group receives usual outpatient care and lifestyle education materials, with the app installed only for rPPG measurement so that digital-biomarker measurement is identical across groups. Clinical assessments (6-minute walk distance, grip strength, blood pressure, blood lipids and metabolic markers), questionnaires (SF-12, PHQ-9, GAD-7, KOSS-24), and digital biomarkers (rPPG-derived heart rate, heart rate variability, respiration, activity) are collected at baseline and at 6 weeks. The primary outcome is the between-group difference in the change in 6-minute walk distance from baseline to 6 weeks. Because this is an exploratory pilot, the results are intended to estimate the effect size and variance for a future definitive randomized controlled trial, and to assess the validity of digital biomarkers as well as the safety, feasibility, and adherence of the program.