**6.1 Diastole**

During the diastolic phase, blood flows into the right atrium from the superior and inferior vena cava, which elevates the internal pressure of the right atrium. When the right atrial pressure surpasses the right ventricular pressure, the tricuspid valve passively opens, enabling the blood to move toward the right ventricle. Simultaneously, the oxygen-rich blood from the lungs returns to the left atrium, resulting in an


#### **Table 3.**

*The comparative refractory periods of different portions of the heart muscle.*

escalation in left atrial pressure. This leads to the opening of the bicuspid valve, which allows the passage of blood from the left atrium to the left ventricle.

#### **6.2 Systole**

During systole, the right and left ventricles contract and discharge blood into the pulmonary trunk and the aorta respectively. At this time the pulmonic and aortic heart valves open to allow the passage of blood into the pulmonary artery and aorta. However, the bicuspid and tricuspid atrioventricular valves remain closed during this period. But during the closure of these two valves, the first cardiac sound, i.e. the "lub" sound is generated at the beginning of the ventricular systole; and at the end of the ventricular systole, the second heart sound, i.e. the "dub" sound is generated due to the closure of the pulmonic and aortic valves.

So, each cardiac cycle comprises the full contraction and relaxation of both the atria and ventricles and lasts around 0.8 s.

The time periods of the atrial and ventricular events of the cardiac cycle are given below:


### **7. Cardiac output of heart**

The volume of blood that a healthy heart pumps in 1 min is termed as the cardiac output of the heart. Logically, the cardiac output (CO) is equal to the product of the stroke volume (SV) and heart rate (HR). It is expressed in l/min.

```
CO ml ð Þ¼ = min SV ml ð Þ� =beat HR beats ð Þ = min
```
### **8. Pathology of cardiovascular system**

#### **8.1 Diagnosis of cardiovascular diseases**

Diagnosis of CVDs is often conducted by the following approach


*Perspective Chapter: Physiology and Pathology of the Cardiovascular System DOI: http://dx.doi.org/10.5772/intechopen.108355*


#### **8.2 Risk factors of cardiovascular diseases**

The risk factors of CVDs can be categorized into two classes: non-modifiable and modifiable risk factors (**Figure 4**). Non-modifiable risk factors are those that cannot be altered or controlled. These include- ethnicity, race, age, gender, and genetic factors of an individual. On the contrary, modifiable risk factors are those that can be altered or controlled by modifying the lifestyle of an individual. For

**Figure 4.** *Risk factors of cardiovascular diseases (designed with biorender).*

example—smoking cessation, weight control, proper maintenance, and control of lifestyle diseases (e.g. diabetes, hypertension) can significantly reduce the risk of CVDs.
