In order to compare the contribution of atrial relaxation and ventricular contraction in determining systolic atrial filling, the jugular venous blood flow velocity curve was recorded transcutaneously with a directional Doppler flowmeter in 81 cases of arrhythmias involving dissociation between atrial and ventricular activity (A-V block, atrial fibrillation, atrial standstill, nodal rhythm, wandering pacemaker). After a brief historical review of the subject the recorded tracings are analysed and evidence provided for the participation of both cardiac events in achieving normal systolic return.