C enter-based cardiac rehabilitation (CBCR), the gold standard of secondary prevention (SP) of coronary heart disease (CHD), 1 provides irrefutable health benefits. 2 Support for healthy behavior change is a vital component of contemporary CBCR. 3 However, fewer women than men are referred to CBCR 4,5 and as few as 10-20% of women enroll with up to a 56% noncompletion rate. [6][7][8][9] Welldocumented barriers contribute to the underutilization of CBCR 10 including inadequate health insurance and costly copayments. 11 Women with transportation challenges, less social support, family obligations, depression, or anxiety and women of color are least likely to utilize CBCR. 8,[12][13][14] These barriers have prompted the need to redesign and expand SP alternatives for women. [15][16][17] Individualized SP programs that incorporate sex-specific components hold promise for improving the health behaviors of women. [18][19][20] Moreover, mobile health (mHealth) technology has the potential to increase scalability of SP through broader reach seamlessly in daily life and improved intervention effectiveness. 21 Although technology-enhanced home-based cardiac rehabilitation (CR) offers a possible adjunct to poor CBCR participation, 22 evidence for improved reach and effectiveness for women is limited. 23 Theoretically driven mHealth SP interventions designed specifically for women unable to access CBCR are lacking. 24 Our previously developed gender-specific CBCR 25,26 was translated to a gender-specific mHealth SP behavior change intervention, called HerBeat. Descriptions of the theoretical underpinnings, system architecture, and usability testing of our prototype are found elsewhere. 27,28 HerBeat focuses on improving the health behaviors of women (eg, physical activity [PA], eating behavior, and stress management). Our primary aim was to evaluate, in a randomized controlled pilot study, whether participants in the HerBeat compared with participants in the educational usual care (E-UC) group improved exercise capacity (EC) at 3 mo measured by the 6-min walk test (6MWT). Secondary outcomes included PA, blood pressure (BP), resting heart rate (RHR), body mass index (BMI),