Morbid obesity and diabetes cause diastolic dysfunction that can be detected by Doppler echocardiography. Patients with the metabolic syndrome could demonstrate early diastolic dysfunction that may influence effort tolerance. A total of 32 patients (17 men) who fulfilled >/=2 of the 5 metabolic syndrome criteria were studied. The average age of patients was 37+/-2 years. All patients were overweight/obese (mean body mass index of 34.4+/-0.7 kg/m(2)), 15 had blood pressure >130/85 mm Hg, 19 had elevated triglyceride levels (>150 mg/dL), and 17 had low high-density lipoprotein cholesterol levels (men <40 mg/dL, women <50 mg/dL). Maximal exercise was performed using Bruce treadmill protocol with standard stress echocardiography and tissue Doppler. Maximal oxygen consumption (VO(2max)) was measured using indirect calorimetry. Left ventricular filling pressure was indirectly derived from dividing pulse Doppler early mitral inflow velocity (E) by tissue Doppler early diastolic mitral annular motion (E') or E/E'. The group's average treadmill time was 8.06+/-0.28 minutes, VO(2max) was 28.6+/-1.1 mL/kg/min, and 8.2+/-0.3 metabolic equivalents. None had evidence of myocardial ischemia or systolic or diastolic dysfunction with exercise. Mean "resting" E/E' and "post-exercise" E/E' were 7.01+/-0.04 and 7.41+/-0.41, respectively. There was no significant correlation between resting E/E' and VO(2max) (r=-0.266; P=.14). The post-exercise E/E' significantly correlated with VO(2max) (r=-0.483; P=.005) and metabolic equivalents (r=-0.487; P=.005). Diastolic function is preserved in early metabolic syndrome. Even in the normal diastolic function range, exercise E/E' is inversely related to VO(2max). Further longitudinal studies are needed to determine whether they develop diastolic dysfunction and related heart failure.