Angiotensin-converting enzyme 2 (ACE2) is a monocarboxypeptidase that metabolizes several vasoactive peptides, including angiotensin II (Ang-II; a vasoconstrictive/proliferative peptide), which it converts to Ang-(1–7). Ang-(1–7) acts through the Mas receptor to mediate vasodilatory/antiproliferative actions. The renin–angiotensin system involving the ACE–Ang-II–Ang-II type-1 receptor (AT1R) axis is antagonized by the ACE2–Ang-(1–7)–Mas receptor axis. Loss of ACE2 enhances adverse remodeling and susceptibility to pressure and volume overload. Human recombinant ACE2 may act to suppress myocardial hypertrophy, fibrosis, inflammation, and diastolic dysfunction in heart failure patients. The ACE2–Ang-(1–7)–Mas axis may present a new therapeutic target for the treatment of heart failure patients. This review is mainly focused on the analysis of ACE2, including its influence and potentially positive effects, as well as the potential use of human recombinant ACE2 as a novel therapy for the treatment cardiovascular diseases, such as hypertension and heart failure.