1. C ARDIAC C YCLE

2. E ARLY DIASTOLE Pressure in ventricles is low. Pressure difference causes A-V valves to open and the ventricles to fill. 70% of returning blood enters ventricles prior to contraction. Ventricular pressure gradually increases.

3. A TRIAL SYSTOLE Remaining 30% of blood is pushed into the ventricles. Ventricular pressure increases more.

4. I SOVOLUMIC VENTRICULAR CONTRACTION As ventricles contract, ventricular pressure rises sharply. When this pressure exceeds atrial pressure, A-V valves close. Muscles and cords prevent A-V valves from bulging into the atria.

5. V ENTRICULAR SYSTOLE A-V valves remain closed. Atria are relaxed. Pressure in atria is low. Blood flows into atria from veins. (ventricles are contracting, atria are filling) Heart sound: LUBB

6. P ROGRESSING VENTRICULAR SYSTOLE Ventricular pressure increases. When it exceeds pressure in pulmonary trunk (right side) and aorta (left side) pulmonary and aortic valves open. Blood is ejected from each valve’s ventricle and into arteries.

7. B ACK TO THE BEGINNING … Ventricular pressure drops as ventricles begin to relax. When ventricular pressure is lower than the blood pressure in the aorta and pulmonary trunk, pressure difference is reversed. Valves close. As soon as ventricular pressure is less than atrial pressure, the A-V valves open and we start all over again. DUPP

9. P RESSURE AND VOLUME