Heart: Cardiac Cycle

Systemic circulation --> superior/inferior vena cava --> right atrium --> tricuspid valve --> right ventricle --> pulmonary artery --> pulmonary veins --> left atrium --> mitral valve --> left ventricle --> aorta --> systemic circulation

Period of relaxation, during which the heart (ventricles) fill with blood

Period of contraction, during which the heart (ventricles) empty

Depolarization of the atria

Ventricular depolarization

Ventricular repolarization, causing the ventricle to relax

Atria contraction during the last third of ventricular diastole to provide approximately 25% of ventricular filling in each cycle

Short period after ventricular pressure causes the atrioventricular valves to close but before ventricular pressure exceeds that in the great arteries and semilunar valves open

Once ventricular pressure exceeds pressure in the great arteries, this is the first 1/3 of total ejection period when approx 70% of stroke volume is ejected

Last 2/3 of total ejection period when 30% of stroke volume is ejected; ends with closure of the semilunar valves

At the end of ventricular systole, when the semilunar valves have already closed but the atrioventricular valves have not yet opened; ends when atrial pressure exceeds ventricular pressure

The first 1/3 of ventricular diastole, ventricular pressure falls and atrial pressure increases causing the atrioventricular valves to open and most of ventricular filling

Period of relatively little ventricular filling when blood flows directly from veins through atria to ventricles; follows rapid ventricular filling and ends with atrial systole

Backflow of blood in the aorta suddenly ceases when the aortic valve closes, resulting in no more decrease of aortic pressure

Increase in atrial pressure caused by atrial contractionleft atria: 7-8 mmHgright atria: 4-6 mmHg