Heartbeat

The relaxation of heart chambers fills them with blood and contraction of chambers propels blood out of them. The alternating relaxations and contractions make up the cardiac cycle and one complete cardiac cycle makes one heartbeat. Complete cardiac cycle consists of the following steps. 

Atria and ventricles relax and blood is filled in atria. This period is called cardiac diastole. Immediately after their filling, both atria contract and pump blood towards ventricles. This period in cardiac cycle is called atrial systole. Now, both ventricles contract and pump blood towards body and lungs. The T period of ventricular contraction is called ventricular systole. In one heartbeat, diastole lasts about 0.4 seconds, atrial systole takes about 0.1 seconds, and ventricular systole lasts about 0.3 seconds.

When ventricles contract, tricuspid and bicuspid valves close and "lubb" sound is produced. Similarly when ventricles relax, the semilunar valves close and "dubb" sound is produced. "Lubb-dubb" can be heard with the help of a stethoscope.

Heart rate and Pulse rate

Heart rate is the number of times the heart beats per minute. At rest or during normal activities, the normal heart rate is 70 times per minute in men and 75 times per minute in women. The heart rate fluctuates a lot depending on factors such as activity level and stress level.

Heart rate can be measured by feeling the pulse. Pulse is the rhythmic expansion and contraction of an artery as blood is forced through it by the regular contractions of heart. Pulse can be felt at areas where artery is close to skin for example at wrist, neck, groin or top of foot. Most commonly, people measure their pulse in their wrist.

BLOOD VESSELS

The third part of blood circulatory system are blood vessels, which function to transport blood throughout body. The most important vessels in blood circulatory system are arteries, veins, and capillaries. 
Arteries: Arteries are the blood vessels that carry blood away from heart. In adults, all arteries with the exception of the pulmonary arteries, carry oxygenated blood. The structure of arteries is well adapted to their function. The walls of an artery are composed of three layers. The outermost layer is made of connective tissue. 

The middle one is made up of smooth muscles and elastic tissue while the innermost layer is made up of endothelial cells. The hollow internal cavity in which blood flows is called lumen.

When arteries enter body organs, they divide into smaller vessels known as arterioles.Arterioles enter tissues and divide into capillaries.

Capillaries are the smallest blood vessels present in tissues. These are formed by the divisions of arterioles. The exchange of materials between blood and tissue fluid is carried out through capillaries.

The walls of capillaries are composed of only a single layer of cells i.e. endothelium. This layer is so thin that molecules of the digested food, oxygen and water etc. can pass through them and enter tissue fluid. Waste products such as carbon dioxide and use can diffuse from tissue fluid into blood.
-Veins: A vein is a blood vessel that carries blood towards heart. In adults, all veins with the exception of pulmonary veins, carry deoxygenated blood.
Veins are also well-adapted to their function. The walls of vein are composed of the same three layers as are present in artery wall, with the difference that the middle layer of vein has less smooth muscles 
and elastic tissue as compared to artery. So the middle layer of vein is comparatively thin. 
 The lumen of the veins is broader than that of arteries