To study the influence of left ventricular (LV) late diastolic filling on the A wave of the LV pressure, simultaneously recorded echocardiographic LV dimensions and high-fidelity LV pressure measurements were taken in 24 patients. Group I comprised eight patients without LV hypertrophy (LVH) and LV end-diastolic pressure (LVEDP) ≤ 13 mm Hg. Group 2 comprised 16 patients with LVH secondary to aortic stenosis, idiopathic hypertrophic subaortic stenosis, or hypertension and increased LVEDP. Patients in group 2 had significantly thicker left ventricles, decreased mitral E-to-F slopes, and larger A waves in the LV pressure curve. On the basis of end-diastolic chamber stiffness, we divided group 2 into two populations: 12 patients (group 2A) with end-diastolic chamber stiffness similar to that in group 1, and four patients (group 2B) with markedly elevated end-diastolic chamber stiffness. Patients in group 2A had a larger atrial contribution to LV filling than those with markedly abnormal stiffness (group 2B). Therefore, in LVH an increased A wave in the LV pressure may be related to either elevated end-diastolic chamber stiffness or augmented left atrial volume transport.