OBJECTIVE--To study the possible mechanisms underlying the dominant "a" wave in the jugular venous pulse seen in patients with left ventricular hypertrophy (Bernheim "a" wave). DESIGN--Prospective examination of the left ventricular transverse and longitudinal axes, transmitral and transtricuspid flows, and jugular venous pulse recordings. SETTING--Tertiary referral centre for cardiac disease. SUBJECTS--23 patients with left ventricular hypertrophy of various aetiologies and a dominant "a" wave in the jugular venous pulse. Controls were 21 normal volunteers. RESULTS--Early diastolic filling of the right ventricle was normal. During right atrial systole the (mean(SD)) tricuspid ring motion was exaggerated (1.2(0.4) v 0.8(0.2) cm, p < 0.001) and Doppler A wave velocity slightly increased (0.3(0.1) v 0.2(0.08) m/s, p < 0.01), although the E wave remained dominant. By contrast left ventricular isovolumic relaxation time was longer than normal (70(20) v 55(10) ms, p < 0.001) with wall motion incoordinate in the septal long axis, 15%(9.5%) v 6.6%(3%) total excursion occurring before mitral valve opening. During early filling the extent of long axis motion was decreased to 0.6(0.5) cm from 1.1(0.2) cm, (p < 0.001) and 0.5(0.2) cm from 0.9(0.2) cm, (p < 0.0001) at the left and septal sites, and similarly its peak lengthening rate reduced to 5.4(2.5) cm/s from 10(3) cm, (p < 0.001) and 4.3(2.2) cm/s from 8(2) cm, (p < 0.001). The atrial component of long axis lengthening was increased to 43%(18%) from 29%(6%) (p < 0.01) and 55%(15%) from 33%(8%) of the total excursion (p < 0.0001). Left ventricular E/A ratio was less than normal (0.9(0.8) v 1.4(0.4), p < 0.05). CONCLUSIONS--There is no evidence of obstruction or any other disturbance of early diastolic right ventricular inflow in Bernheim's syndrome. It is possible that the haemodynamically appropriate increase in left atrial activity is mirrored on the right side due to shared interatrial myocardial fibres. This could represent a form of atrial interaction.