Lets look now at how pressures change in the heart. Blood coming back to the heart is under low pressure and the pressure in the Superior Venacava is only 13 over 8 mmHg. When the blood comes into the Right Atrium it is still about the same pressure. Next the blood flows through the Tricuspid Valve and into the Right Ventricle. The Right Ventricle is a pumping chamber. It squeezes the blood with some force generating high pressure at about 30 over 8 mmHg. The blood then goes on to the Lungs under pressure of 30 over 17. As it is pumped through the lungs it looses most of its pressure and when it reaches the Left Atrium it is under low pressure at 17 over 12. When the blood gets into the Left Ventricle which has the strongest walls. The Left Ventricle squeezes around it generating very high pressure at 120 over 10. This pressure pushes the Aortic Valve open and the blood moves on to the Aorta which is under pressure of 120 over 70. This pressure in the Aorta (120 over 70) is the same pressure that is in your arms.

Look at the pressure waves in the heart. Notice that the pressure in the Right Atrium is the lowest followed by the a higher pressure in the Right Ventricle. The pressure in the Left Atrium is a little bit higher that the Right Atrium. The pressure in the Left Ventricle is the highest.