Clinical congestive heart failure (CHF) is traditionally associated wtih significant left ventricular (LV) systolic dysfunction. Over a 1-year period, 58 patients with CHF and intact systolic function (LV ejection fraction [EF] 62 +/- 11%) were identified. An objective clinical-radiographic CHF score was used to document the clinical impression. Based on radionuclide evaluation of peak filling rate, 38% of these patients were found to have a significant abnormality in diastolic function as measured by peak filling rate (less than 2.50 end-diastolic volume/s). An additional 24% of the patients had probable diastolic dysfunction with borderline abnormal peak filling rate measurements (2.5 to 3.0 end-diastolic volume/s). The disease states most frequently associated with CHF and intact systolic function were coronary artery disease and systemic hypertension. During a 3-month sampling period 42% of patients with clinical diagnosis of CHF referred to the nuclear cardiology laboratory were found to have intact systolic function; thus, intact systolic function is not uncommon in patients with clinical CHF. Abnormal diastolic function is the most frequently encountered mechanism for the occurrence of CHF. Definition of systolic and diastolic function appears relevant for development of optimal therapeutic strategies for the treatment of patients with CHF.