Personal Activity Intelligence (PAI) is a novel heart-rate-based metric used to assess cardiorespiratory fitness and quantify physical activity. The aim of this study was to examine the feasibility, acceptability, and effectiveness of PAI with patients in a clinic setting. Patients (n = 25) from 2 clinics underwent 12 weeks of heart-rate-monitored physical activity interfaced with aPAI Health phone app. We used a pre-post design with the Physical Activity Vital Sign and the International Physical Activity Questionnaire. Feasibility, acceptability, and PAI measures were used to evaluate the objectives. Twenty-two patients (88%) completed the study. There were significant improvements in International Physical Activity Questionnaire metabolic equivalent task minutes per week ( P = .046) and a decrease in sitting hours ( P = .0001). The Physical Activity Vital Sign activity increase in minutes per week was not significant ( P = .214). Patients achieved a mean PAI score of 116 ± 81.1 and 100 or greater 71% of the days. Most patients (81%) expressed satisfaction with PAI. Personal Activity Intelligence is feasible, acceptable, and effective when used with patients in a clinic setting.