ABSTRACT Cardiac rehabilitation (CR)—which involves exercise training, patient education, and health behavior modification—is a comprehensive intervention traditionally delivered in clinic-based settings, with the highest recommendation and level of evidence classification (i.e., Class I, Level A) for secondary prevention. Traditional CR significantly reduces rates of reinfarction (by 47%) and both cardiac (36%) and all-cause mortality (26%) in acute coronary syndrome (ACS) survivors, an extremely sedentary population whose functional status and health-related quality of life (HRQOL) improve after CR participation. Despite the well-established effectiveness of traditional CR—benefits achieved through continued program participation (i.e., adherence), fewer than 10% of eligible ACS patients in the US who initiate CR (<30%) attend all prescribed CR sessions, with even lower rates among non-Hispanic Black and Hispanic patients. Dismal participation in traditional CR programs and utilization disparities that have endured for decades highlight the need to design nontraditional CR models (e.g., virtual, hybrid) and rigorously test whether such models can deliver the same quality of traditional CR while improving patient participation among varied groups of cardiac patients. To address this need, our group combined user-centered design (UCD) and implementation science (ImS) principles and methods to design and test the feasibility of a telehealth-enhanced hybrid CR program (TeleheartCR; mixture of in-person, clinic and virtual, home sessions with a telehealth platform that supports real-time monitoring and electronic health record [EHR] data integration). This program targets patient- and provider-level barriers in a large hospital setting that serves patients from varied backgrounds. Now, we propose to conduct a single-site, single-blind, two- arm, parallel group, randomized controlled trial to determine the degree to which TeleheartCR improves CR participation and clinical outcomes relative to traditional CR among ACS patients. We hypothesize that participants allocated to TeleheartCR will demonstrate greater program adherence (% of CR sessions completed) and non-inferior functional capacity (pre-to-post program change in six-minute walk test [6MWT] distance) vs participants allocated to traditional CR. Both CR programs include 24 CR sessions over 3 months. Program attendance, and a 6MWT at baseline and program completion, will be collected and extracted from the EHR. Self-reported program acceptability, appropriateness, and HRQOL will be secondary outcomes. We will also explore the comparative costs and cost-effectiveness (TeleheartCR vs. traditional CR), as well as whether non-Hispanic Black, Hispanic, and low socioeconomic status patients particularly benefit. Findings will inform the design and implementation of innovative hybrid delivery models to achieve broader utilization of established interventions in hospital settings that serve patients fr...