Cardiac Cycle and Cardiac Output

relaxation (diastole)

• begins at the end of a cardiac cycle

• all 4 chambers are in diastole

• initiated by repolarization of ventricles

• ventricular pressure decreases and atrioventricular valves open and ventricles fill

Atrial systole

• action potential from SA node causes a trail depolarization

• atria contract and complete filling of the ventricles

• Atrioventricular valves still open, semilunar valves still closed

Ventricular systole

• contraction of ventricles; pushes blood against Atrioventricular valves forcing them shut 

• ventricular pressure increases, semilunar valves open, ejection of blood

Cardiac Cycle total time

0.8-0.9 seconds

Atrial Systole time

0.1 sec

Ventricles contracting + ventricular systole

0.3 sec

relaxation/refilling diastole

0.5 sec

systemic circulation

left side of the heart pumps blood through vessels to the tissues of the body and back to the right side of the heart

pulmonary circulation

right side of the heart pump blood through vessels to lungs and back to the left side of the heart

cardiac output

volume of blood pumped from the heart per minute (mL/min)

cardiac output

stroke volume in mL/beat (SV) x heart rate in bpm

stroke volume

amount of blood pumped per ventricle per contraction

heart rate

number of beats/contractions of ventricles per minute