Adherence to medication is crucial to improve clinical outcomes in patients with heart failure (HF). However, at least 1 out of 4 patients is nonadherent to his or her medication. Several studies have quantified medication adherence in HF patients, monitoring only 1 drug with the Medication Event Monitoring System (MEMS). Some authors have argued that monitoring 1 drug reflects the whole adherence behavior, although there is some evidence of important differences in adherence to distinct drug classes. Furthermore, medication characteristics could be a relevant predictor of adherence, and different drugs could pose different barriers to patients.