Cardiac

Heart Sounds

  • “Lub-dup”

    • Lub (S₁): closure of AV valves (start of systole).

    • Dup (S₂): closure of SL valves (start of diastole).

  • Abnormal sounds = murmurs (valve problems).

Cardiac Cycle

  • One complete heartbeat (systole + diastole of atria & ventricles).

  • Average: 0.8 sec at 75 bpm.

  • Phases:

    1. Atrial systole: atria contract; blood pushed into ventricles.

    2. Ventricular systole: ventricles contract; AV valves close → isovolumetric contraction → SL valves open → blood ejected.

    3. Ventricular diastole: relaxation; SL valves close → isovolumetric relaxation → AV valves reopen → filling begins.

120 mm

Depolarize before the contraction 

Diastole the pressure of aorta is 80

❤ Cardiac Cycle in Order

1⃣ Ventricular Filling (During Ventricular Diastole)

  • Both atria and ventricles are relaxed.

  • AV valves (tricuspid & mitral) are open → blood flows passively from atria to ventricles.

  • Semilunar valves (aortic & pulmonary) are closed.

  • Near the end, atria contract to push the last bit of blood into ventricles → this is called atrial systole.

✅ Summary: Ventricles fill with blood → atria contract to top them off.

2⃣ Ventricular Systole (Ventricular Contraction)

This step actually has two parts:

a. Isovolumetric Contraction

  • Ventricles start to contract.

  • Pressure rises → AV valves close (first heart sound “lub”).

  • Semilunar valves still closed, so no blood leaves yet.

b. Ventricular Ejection

  • Once ventricular pressure is higher than pressure in the aorta/pulmonary trunk → semilunar valves open.

  • Blood is pumped out of the ventricles.

✅ Summary: Ventricles contract → blood is ejected into aorta & pulmonary trunk.

3⃣ Early Diastole (Isovolumetric Relaxation)

  • Ventricles relax after contraction.

  • Semilunar valves close (second heart sound “dup”).

  • AV valves are still closed → pressure drops quickly inside ventricles.

  • When ventricular pressure falls below atrial pressure → AV valves open, starting the next cycle (ventricular filling again).

✅ Summary: Ventricles relax → semilunar valves close → pressure falls → AV valves reopen → cycle repeats.