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Background: Cardiovascular disease (CVD) patients are at increased risk for mortality due to the progression of the disease and complications associated. Exercise has been shown to help improve cardiorespiratory fitness and to decrease mortality risk. Moderate continuous training (MCT) is currently the staple form of exercise for secondary prevention of CVD complications. Research has recently shown support for high-intensity interval training (HIIT) as an alternative to MCT, however, limited research exists regarding the extent of efficacy of HIIT versus MCT for improving cardiorespiratory fitness. The link between specific exercise regimens and their effect on decreasing mortality risk needs to be better understood by providers in order to provide stronger clinical recommendations to CVD patients. Purpose: To investigate the effect of HIIT versus MCT for all populations of CVD patients in reducing mortality risk, and for what period of time maintaining a HIIT regimen continues to have benefits for mortality risk. Methods: A systematic review was conducted utilizing PubMed, Google Scholar, ProQuest, and MEDLINE Complete, searching from inception to February 2020. Articles selected compared HIIT versus MCT interventions and included effects on individuals diagnosed with CVD. Three researchers conducted independent searches, with review of titles, abstracts, and full articles. A second researcher duplicated the review process for each title, abstract, and full article found. A quality assessment and qualitative analysis were then created and developed for the included studies. Results: Four studies, including a total of 3,588 participants between all four, were included in the qualitative analysis. HIIT was found to be superior to MCT for improving cardiorespiratory fitness, measured specifically in VO2Peak (95% confidence interval), in all four studies. HIIT HIIT VS MCT FOR MORTALITY DECREASE IN CVD v was also found to improve BP, HDLs, LDLs, CO, ASP, ADP, PGC-1a, total and LVEF, and arterial stiffness, which are all factors known to improve cardiac health and decrease mortality. A definitive duration of benefits from HIIT was not found from this research. Conclusion: HIIT is superior to MCT for improving cardiorespiratory fitness for CVD patients, particularly in a short-term six to twelve-week period. Additional research is required to determine optimal details regarding specific HIIT programs and to which populations HIIT is effective for, including females and the elderly.