We studied the relation between relative wall thickness, left ventricular systolic pump performance, and myocardial contractile function in 77 older patients with normal ejection fraction who were free of valvular and myocardial ischemic disease. Group 1 comprised 49 patients with relative wall thickness > or = 0.45; group 2 (n = 28) had normal relative wall thickness. Pump performance was characterized by stroke volume index, cardiac index, and stroke work; myocardial function was characterized by midwall shortening and circumferential stress versus shortening relations. Group 1 patients had lower end-diastolic volume (83 +/- 3 vs 124 +/- 5 ml, p < 0.05), cardiac index (2.6 +/- 0.2 vs 3.5 +/- 0.1 L/min/m2, p < 0.05), and stroke work/100 g left ventricular mass (43 +/- 2 vs 53 +/- 3 g-m/100 g, p < 0.005). Although there was no significant difference with regard to ejection fraction or fractional shortening at the endocardium, fractional shortening at the midwall was significantly lower in group 1 than in group 2 (16 +/- 1% vs 19 +/- 1%, p < 0.005). This lower value for midwall shortening was observed despite lower values for endsystolic stress, implying decreased myocardial contractile function. Lower stroke volume index in group 1 patients, likely due to small chamber size, was not offset by increased heart rate, resulting in a low-normal cardiac index; in 33% of group 1 patients, cardiac index was < 2.2 L/min/m2, indicating reduced pump performance. Our data indicate an abnormality in pump performance and myocardial function in patients who have high relative wall thickness and normal ejection fraction.