Introduction: The needs for advanced care planning, including preferences to life-sustaining treatments (LSTs), in patients with heart failure (HF) are comparable to or higher than those in cancer survivors, but they had less access to such care than cancer survivors. Diagnostic context and patients’ attitudes and perceived susceptibility can impact preferences to LSTs, but there is limited evidence on these relationships. Purpose: To compare LST preferences, attitudes, and perceived susceptibility between patients with HF and cancer survivors, and to examine the associations of these variables with their preference for each LST (cardiopulmonary resuscitation [CPR], ventilation support, hemodialysis, and hospice care). Methods: Secondary data on LST preferences (the Korean-Advance Directive), attitudes toward advance directive (Advance Directive Attitude Survey), perceived susceptibility (Perceived Susceptibility subscale of the Advance Care Planning survey), and demographic characteristics were obtained from 36 outpatients with HF (mean age, 65.44 years; male, 69.4%) and 107 cancer survivors (mean age, 67.39 years; male, 32.7%). To compare LST preferences, attitudes, and perceived susceptibility between the wo diagnostic groups, chi-square test, t -test, and Wilcoxon rank sum test were used. To examine the relationships of diagnostic context, attitudes, and perceived susceptibility to preferences for each LST, controlling for sex, marital status, and educational level, multivariable logistic regression analyses were used. Results: More patients with HF preferred CPR than cancer survivors (41.7% and 15.9%, χ 2 = 8.88, P = 0.003). Attitudes and perceived susceptibility were similar between the two diagnostic cohorts ( P = .508 and P = .062, respectively). Patients with HF had greater odds of preferring CPR (odds ratio [OR] = 3.02, confidence interval [CI] = 1.19, 7.70) than cancer survivors. Patients with more positive attitudes had greater odds of preferring hospice care (OR = 1.14, CI = 1.06, 1.23). Conclusions: Diagnostic context and patients’ attitudes were associated with preferences for LSTs. Therefore, diagnostic context and improvement in attitudes need to be considered to facilitate informed decision-making for LSTs.