Since the publication of the first systematic review in the late 1980s,1 the efficacy rationale for cardiac rehabilitation (CR) has evolved from a singular outcome of allcause mortality to additional multiple outcomes including cardiac mortality, quality of life, cardiorespiratory fitness (CRF), and cost savings in the form of preventing hospital readmissions.2 In the past decade, the case for the efficacy of reduced all-cause mortality has been challenged,3,4 but two questions arise around this matter: first, has some of the effective potency of exercise-based CR been lost due to modern cardiovascular health promotion and standards of medical, pharmacological, and surgical interventions being much improved5? Second, in research trials and in practice, has sufficient fidelity to an appropriate exercise dose been achieved, especially in those reports that have challenged the efficacy of CR4? In light of these questions, there has been a contemporary move to substantiate the efficacy of CR based on reduced hospital readmissions, health care costs, and quality of life.2 Given that a number of reviews, letters to editors, post hoc trials, and audit-data analyses have raised the question of exercise program dose fidelity,6,7 the aim of the current study was to investigate the influence of exercise fidelity on measures of CRF (incremental shuttle-walk test and heart rate walking speed index [HRWSI]) when patients were actively encouraged to achieve intensities >50% heart rate reserve (HRR).