It has been shown recently that the handgrip-apexcardiographic test (HAT) represents a new mode of stress test, which shows a high sensitivity in identifying coronary patients by assessing exercise-induced ischemic left ventricular diastolic abnormalities. To assess the prevalence of left ventricular diastolic abnormalities and the usefulness of HAT as a diagnostic tool in patients with syndrome X (angina pectoris in the presence of normal coronary arteries), HAT was obtained in 275 clinically normal subjects and in 9 patients who presented with typical chest pain and who were subsequently found to have a positive treadmill ECG test and no coronary artery disease by angiography. As diastolic indices served: the relative A wave to total height (A/H) and to diastolic amplitude (A/D) of the apex tracing, the total apexcardiographic relaxation time (TART), TART corrected for the duration of diastole (TARTI) and the diastolic amplitude time index [DATI = TARTI/(A/D)]. Positivity of HAT was defined by the presence of at least one of the following recently introduced criteria: (1) A/H during or after handgrip > 21%, (2) TART during handgrip > TART at rest > 143 ms or/and TARTI during handgrip < 0.14 or (3) DATI during handgrip < 0.27. At rest, in 6/9 (67%) patients all variables were within normal limits, whereas in 3/9 (33%) patients an abnormal A/H or TARTI was observed. During and after handgrip, however, all patients showed abnormal changes in at least two diastolic variables, DATI and A/H being most frequently abnormal (67 and 56%, respectively). Further, using the above-mentioned positivity criteria, all patients had a positive HAT result. It can be concluded that according to our present findings an exercise-induced diastolic dysfunction is frequently present in syndrome X patients. Furthermore, using diastolic abnormalities as cutoff points and criteria of positivity, HAT shows a 100% sensitivity for detecting patients with this clinical setting.