Cardiac rehabilitation (CR) programs usually consist of moderate intensity exercise sessions for the purpose of enhancing the physiological and psychosocial status of cardiac patients. It has been postulated that interval training is superior to the traditional continuous training in CR. Most of studies of interval training in cardiac patients have relatively small sample sizes, diverse training methodologies, and included heart failure patients. Furthermore, there have been relatively few comparisons of interval versus continuous exercise in a real life, center-based CR setting. This PhD thesis reports a single–site, randomized controlled trial of aerobic interval training in CR that was undertaken to address some of these concerns. Following 4 weeks of adjustment in the center, 84 coronary artery disease patients were randomly assigned to either an interval exercise group (IE) or a continuous exercise group (CE). Functional capacity, clinical outcomes and quality of life (QoL) were assessed at baseline and after 12 weeks of training. Both groups exercised twice a week under supervision at the center. The CE group exercised continuously at a moderate intensity (50-60% VO2max), whereas the IE group performed 2 minutes of low intensity (40-60% VO2max) followed by 2 minutes of moderate-high intensity (60-85% VO2max) interchangeably. Both groups increased VO2 peak significantly after training; however, IE was no better than CE at eliciting an improvement. In contrast, IE did elicit a significantly greater improvement in maximal power measured during cardiopulmonary exercise testing (CPET), as well as significant reductions in several sub-maximal variables. Some cardiac related risk factors, such as waist circumference, HbA1c% and hs-CRP were reduced in the IE group alone; however some of these changes do not seem to be clinically important. Next, measurements were repeated at 9 months to determine whether or not any of the training induced changes persisted at 6 months follow-up. Peak VO2 remained significantly higher versus baseline within the IE group only. High sensitivity (hs)-CRP was increased in the former CE group, and HDL-C was improved in the former IE group from 3 to 9 months. Finally, a single-group analysis (i.e. regardless of training modality) was undertaken to identify the best predictors of improvement functional capacity in cardiac patients. It was found that the magnitude of change in peak VO2 is dependent upon 6 factors: baseline body fat percentage, baseline left ventricular ejection fraction (LVEF), baseline fitness level, maximal rate pressure product during CPET, baseline psychological state, and number of exercise sessions completed. These observations indicate that interval training in a real life CR setting does not necessarily elicit higher peak VO2, but that it may have some superiority over continuous training in relation to exercise tolerance and performing daily activities. Furthermore, favorable changes may be preserved for up to 6 months following interval training. Finally, several factors that influence the magnitude of improvement in functional capacity following exercise training in CR patients have been identified. Using these factors, CR professionals may be able to identify those cardiac patients for whom the chances of improving functional capacity is low. Furthermore, it may be possible to focus on some of these factors in order to improve the prognosis for patients undergoing CR.