Disruption of leptin signaling is associated with obesity, heart failure, and cardiac hypertrophy, but the role of leptin in cardiac myocyte apoptosis is unknown. We tested the hypothesis that apoptosis increases in leptin-deficient ob/ob and leptin-resistant db/db mice and is associated with aging and left ventricular hypertrophy, increased DNA damage, and decreased survival. We studied young (2- to 3-month-old) and old (12- to 14-month-old) ob/ob and db/db mice and wild-type (WT) controls (n=2 to 4 per group). As expected, ventricular wall thickness and heart weights were similar among young ob/ob, db/db, and WT mice, but higher in old ob/ob and db/db versus old WT. Young ob/ob and db/db showed markedly elevated apoptosis by TUNEL staining and caspase 3 levels compared with WT. Differences in apoptosis were further accentuated with age. Leptin treatment significantly reduced apoptosis in ob/ob mice both in intact hearts and isolated myocytes. Tissue triglycerides were increased in ob/ob hearts, returning to WT levels after leptin repletion. Furthermore, the DNA damage marker, 8oxoG (8-oxo-7,8-dihydroguanidine), was increased, whereas the DNA repair marker, MYH glycosylase, was decreased in old ob/ob and db/db compared with old WT mice. Both ob/ob and db/db mice had decreased survival compared with WT mice. We conclude that leptin-deficient and leptin-resistant mice demonstrate increased apoptosis, DNA damage, and mortality compared with WT mice, suggesting that normal leptin signaling is necessary to prevent excess age-associated DNA damage and premature mortality. These data offer novel insights into potential mechanisms of myocardial dysfunction and early mortality in obesity. © 2006 American Heart Association, Inc.