Development and Evaluation of a Patient–Family Caregiver Dyad mHealth Intervention for Heart Failure Self-Care: Quasi-Experimental Study - Youn-Jung Son; JiYeon Choi; Hyue Mee Kim; Hoyoun Won; Jong-Chan Youn; Sang-Wook Kim; Wang-Soo Lee; Jun Hwan Cho; Kyung‑Taek Park; Joonhwa Hong; Da-Young Kim (Journal of Medical Internet Research)