Patients with signs and symptoms of heart failure and a preserved left ventricular (LV) systolic function may have significant abnormalities in diastolic function. This condition is called diastolic heart failure (DHF) and is observed in about 40% of patients with chronic heart failure (CHF). Diabetes mellitus is one of the major risk factors for DHF. Diastolic dysfunction is observed in about 40% of patients with diabetes mellitus and correlates with poor glycemic control. Suggested mechanisms for diastolic dysfunction in the diabetic heart are: (i) abnormalities in high-energy phosphate metabolism; (ii) impaired calcium transport; (iii) interstitial accumulation of advanced glycosylation end products; (iv) imbalance in collagen synthesis and degradation; (v) abnormal microvascular function, (vi) activated cardiac renin-angiotensin system; (vii) decreased adiponectin levels; and (viii) alteration in the metabolism of free fatty acids and glucose. Because most large, randomized clinical trials in CHF have enrolled only patients with systolic dysfunction, the specific management of diastolic dysfunction is largely unknown. The CHARM-Preserved (Candesartan in Heart Failure: Assessment of Reduction in Mortality and Morbidity-Preserved) trial, the only mega trial specific for DHF (LV ejection fraction >40%), showed that the angiotensin II type 1 receptor antagonist (angiotensin receptor blocker [ARB]) candesartan cilexetil reduced hospital admissions for CHF but not cardiovascular death. Currently, the pharmacologic treatment used in systolic heart failure is also recommended in DHF and includes administration of diuretics and nitrates for pulmonary congestion, and long-term management with ACE inhibitors, ARBs, aldosterone antagonists, and β-adrenoceptor antagonists. Poor glycemic control is associated with a high incidence of heart failure in diabetic patients, but the preferable antihyperglycemic regimen for DHF in patients with diabetes mellitus needs to be determined in further studies.