The metabolic syndrome (MS) is linked to cardiovascular risk. Recently, the Adult Treatment Panel (ATP) III provided new criteria for the definition of the MS. We analyzed the impact of the MS on cardiac structure and function and the independent association of the 5 different components of the ATP III-defined MS with cardiac markers of preclinical disease. Echocardiographic examination was performed in 612 nondiabetic participants with ATP III-defined MS and in 824 participants without the MS. Participants with the MS were more often women (p <0.001) and had similar ages compared with those without the MS. After controlling for confounders, participants with the MS had greater left ventricular (LV) dimension, mass, and relative wall thickness, and left atrial diameter (all p </=0.01), and a higher prevalence of LV hypertrophy (p <0.001), with lower ejection fraction (p <0.05), midwall shortening (p <0.001), and mitral E/A ratio (p <0.05) than participants who did not have the MS. In multiple regression modeling, high blood pressure (BP) and abdominal obesity were the only components of the MS associated with increased LV diameter; only high BP was associated with increased LV mass and prevalence of LV hypertrophy (both p <0.001). When high to normal BP was present in the absence of hypertension, the MS exhibited LV geometry similar to hypertensive participants without the MS. Therefore, abnormal LV geometry and function are related to the MS. Increased BP is the component of the MS most strongly associated with cardiac markers of preclinical disease, even in the absence of traditionally defined hypertension.