Cardiac cachexia remains a phenomenon seen more particularly in New York Heart Association Classification class III or IV heart failure patients. This is frequently missed and written off as "old age." It has a mortality rate of 50% within 18 months of diagnosis, so it is imperative to diagnose cardiac cachexia promptly. It remains elusive in the complexity of its underlying pathophysiology, from cytokine release from both the endocardium and the gut, with systemic implications. This review provides an analysis of cardiac cachexia: (1) definition and diagnostic criteria; (2) prevalence and mortality outcomes; (3) pathophysiology: biomarkers, neurohormonal activation, inflammatory cytokines, involvement of the gut, and iron deficiency anemia; (4) potential of reversibility; (5) differentiating cardiac cachexia from sarcopenia and frailty; (6) treatment: both pharmacologic and nonpharmacologic. This complex disease remains underrecognized.