BACKGROUND: There are limited data on the efficacy of smartphone-based personal health records (PHRs) in patients with cardiovascular disease. This study aimed to examine the processes, outcomes and challenges associated with the implementation of integrated PHRs in patients with heart failure (HF) or coronary artery disease (CAD). METHODS: This prospective single-group study evaluated the effects of a PHR system with the capability to capture electronic health records and vital signs in patients with HF or CAD. The outcomes measured were the 6 -month changes in blood pressure (BP), body weight (BW), brain natriuretic peptide (BNP) levels, lipid profiles and haemoglobin (Hb) A1c levels. RESULTS: Between June 2021 and March 2022, we enrolled 111 patients (median age: 61 years and 47% women) with CAD and/or HF. Over 6 months, the PHR review count distribution was skewed: median 749 times (lowest 2, highest 5724)/180 days, suggesting both low and excessive PHR users. After 3 days, 23% of the patients discontinued inputting their vital signs and medication status. At 6 months, compared with patients who discontinued, those who continued to input their vital signs (N = 86) showed a significant decrease in their systolic BP and LDL-C levels but not in the diastolic BP, BW, BNP, HDL-C, triglyceride or HbA1c levels. CONCLUSIONS: The implementation of smartphone-based PHRs in daily practice is challenging for patients with HF or CAD. However, we observed positive indications of the benefits of PHR in these patients. TRIAL REGISTRATION NUMBER: UMIN000044369.