Purpose <p>Major depressive disorder can exacerbate morbidity and hasten mortality from cardiac disorders among geriatric patients, so mitigation of subthreshold depression (StD) may help improve long-term outcome. Subliminal priming with supraliminal reward stimulation (SPSRS), in which subjects view videos with embedded positive words, may be an effective intervention strategy for StD symptom reduction. The purpose of this pilot randomized controlled trial (RCT) was to evaluate the feasibility of an SPSRS intervention for older patients with cardiac disease and StD admitted to acute care wards.</p> Methods <p>Thirty older patients with cardiac disease and comorbid StD (79.2 ± 7.55&#xa0;years, six female) were randomly assigned to the intervention (SPSRS) group (<i>n</i> = 15) or the control group (<i>n</i> = 15). The intervention group viewed 10-min videos containing positive word stimulation once per day for 5 consecutive days, while the control group viewed YouTube videos containing no positive word stimulation following the same protocol. The primary outcome was a change in score on the Japanese version of the Beck Depression Inventory-II (BDI-II).</p> Results <p>There were no dropouts and no adverse events during the trial. Linear mixed models showed no significant improvement in BDI-II in the intervention group compared to the control group (<i>P</i> = 0.72).</p> Conclusions <p>This pilot RCT supports the feasibility of the SPSRS intervention for older patients with cardiac disease and StD.&#xa0;A full-scale RCT would require a larger sample size, modifications to the content for this patient group, increased frequency of daily interventions, and a more sensitive depression symptom assessment tool.</p> <p>Trial registration: The University Hospital Medical Information Network (UMIN) Registered 8 September 2023 (UMIN000052155).</p>