Influence of Atrial Systole on Effective Ventricular Stroke Volume

The influence of atrial systole on forward or effective ventricular stroke volume at different heart rates and at constant cardiac output was investigated in an open chest dog preparation. The procedure employed allowed a ventricular ejection preceded by an atrial systole to be followed by one which was not. A comparison was made between the effective ventricular stroke volumes of these two ejections. The observations support the view that atrial systole plays a significant role in determining effective ventricular stroke volume and that its influence is greater at higher heart rates when cardiac output is kept constant and stroke volume decreases. The data indicate further that the decrease in effective ventricular stroke volume is due to both a decreased ventricular filling and initial atrioventricular regurgitation.