||Heart failure (HF) is a significant health care problem in the United States. Many patients advance towards end stage HF despite optimal medical therapy. For patients with end stage HF, unfortunately, therapeutic options are limited. While heart transplantation is the most proven treatment for improving survival, it is only performed in approximately 2,500 cases annually due to a shortage of donor hearts. Left ventricular assist device (LVAD) implantation is an FDA-approved therapy and is clinically indicated for two applications: (i) bridge-to-transplantation (BTT) for patients who are awaiting heart transplantation and (ii) destination therapy (DT) for patients who are ineligible for heart transplantation. Unexpectedly, patients in BTT and DT experience cardiac functional recovery after LVAD-induced unloading, which led to an investigational concept called bridge-to-recovery (BTR). For successful clinical translation, it is important to identify reliable predictors and discriminate responders from non-responders. Myocardial fibrosis, as a marker of adverse structural remodeling, is a proven predictor of poor outcomes. Cardiac magnetic resonance (CMR) is a proven and safe imaging modality for non-invasive assessment of myocardial fibrosis. Particularly, cardiac T1 mapping has been widely used for assessment of diffuse myocardial fibrosis. However, current cardiac T1 mapping techniques are unlikely to produce accurate results in LVAD candidates due to three obstacles: arrhythmia, limited breath-hold capacity, and implantable defibrillators. In response, this dissertation describes the development of new cardiac T1 mapping methods that overcome these obstacles. To overcome arrhythmia and limited breath-hold capacity, we developed a new arrhythmia-insensitive-rapid (AIR) cardiac T1 mapping pulse sequence using a robust saturation radio-frequency (RF) pulse that is inherently insensitive to arrhythmia. We also made the AIR pulse sequence rapid by acquiring only one proton-density and one T1-weighted image within a short breath-hold duration of only 2-3 heartbeats. To overcome the challenge of suppressing image artifacts induced by implantable defibrillators, we developed a new wideband AIR cardiac T1 mapping pulse sequence by incorporating a new saturation RF pulse that extends the frequency bandwidth to off-resonant spins induced by defibrillators. The AIR and wideband AIR pulse sequences are validated extensively through in vitro and in vivo experiments.