What happens to the heart when it is relaxed?

During relaxation, also known as diastole, several significant events occur in the heart:

1. Filling of the Heart: The heart relaxes and its chambers expand. As a result, blood flows into the heart from the veins. The right atrium receives oxygen-depleted blood from the body, while the left atrium receives oxygenated blood from the lungs.

2. Atrioventricular Valves Open: The atrioventricular valves (tricuspid valve on the right side and mitral/bicuspid valve on the left side) open, allowing blood to flow freely from the atria into the ventricles.

3. Ventricles Fill: The ventricles continue to fill with blood until they reach their maximum capacity. This phase is known as ventricular diastasis, where the heart muscle is completely relaxed and the ventricles are at their largest volume.

4. Electrical Repolarization: While the heart is relaxed, the cardiac muscle cells undergo electrical repolarization. During this phase, the electrical signals generated during systole (contraction) gradually return to their resting state, preparing the heart for the next contraction.

5. Preparation for Contraction: As diastole ends, the heart muscle prepares for the next contraction (systole). The calcium ions that were released during systole are actively transported back into the sarcoplasmic reticulum, and the myofilaments relax.

6. Atrioventricular Valves Close: Just before the onset of the next contraction, the atrioventricular valves close, preventing backflow of blood from the ventricles into the atria.

The relaxation phase is crucial for the heart to fill with blood and prepare for the subsequent contraction. Proper relaxation ensures that the heart can maintain a regular and efficient pumping rhythm, delivering oxygen-rich blood to the body and removing waste products.