Electrocardiograms and M-mode echocardiograms were evaluated in lean and obese patients, either normotensive or hypertensive, who were paired for mean arterial pressure, age, and sex. Electrocardiographic evidence of left atrial abnormalities (LAA) occurred more frequently (p less than 0.01) and left atrial size was greater in the obese than in the lean patients (p less than 0.01). The left atrial emptying index, an indicator of early diastolic ventricular function, was reduced in obese patients (p less than 0.01), most markedly in those with obesity-hypertension. The left atrial emptying index was reduced in obese patients with electrocardiographic LAA compared to obese patients without this electrocardiographic sign (p less than 0.02). A close correlation (r = 0.61, p less than 0.001) was obtained between the left atrial emptying index and atrial ECG abnormalities. These left atrial abnormalities in obesity and particularly in obesity-hypertension indicate diastolic ventricular dysfunction.