Left ventricular dynamics of trained dogs anesthetized with methohexital

The cardiac response to intravenous administration of the ultrashort-acting oxybarbiturate anesthetic, methohexital sodium, was studied in trained dogs. Heart rate increased immediately and gradually declined to the control value 60 minutes later. Stroke volume decreased immediately, reversed transiently, and decreased again, to return gradually to the control value at one hour. Peak aortic flow velocity and peak aortic flow acceleration paralleled the triphasic response of stroke volume. Cardiac output decreased initially, then increased to above the control value to a maximum at the time of maximum heart rate, then decreased again to below the control value by 30 minutes. From 30 minutes to 60 minutes cardiac output gradually returned to the control value.