In response to the increasing demand for noninvasive physiological monitoring in dementia care, particularly with horticultural therapy, in this study, we evaluated the feasibility of Eulerian video magnification (EVM) for contact-free heart rate estimation. Utilizing dorsal hand imagery from older adults with dementia, we compared two region-of-interest (ROI) selection strategies against electrocardiography (ECG) benchmarks. Empirical results indicated that the large-area ROI strategy outperformed the small-area alternative, yielding a lower mean absolute error of 9.00 bpm and a stronger correlation trend with ECG data (ρ = 0.516, p = 0.059). This performance advantage is primarily due to the spatial averaging effect, which effectively mitigates noise from skin heterogeneity, specular reflections, and microtremors characteristic of this demographic. Overall, integrating EVM with dorsal hand imaging demonstrates preliminary feasibility for clinical monitoring. Future research should prioritize expanding cohort sizes and validating signal robustness within dynamic horticultural environments to ensure practical therapeutic utility.