The ventricles then pump the blood to the lungs and the rest of the body. More about Structure of the heart . The number of times that the heart beats in a minute. A normal heart rate increases and decreases, depending on how strenuous one's activity level is. One's heart rate when sleeping is typically lower than when walking or running.
Emotional changes can also cause one's heart rate to increase.
See also bradycardia , tachycardia . These valves open to ensure that blood flows into the heart chambers as needed, and they close to ensure that blood does not flow back into the heart after it has been pumped out to the lungs and body. More about How your heart works . A heartbeat consists of the contraction of the atria, quickly followed by the contraction of the ventricles. May be caused by several factors including the immune response, bacterial or viral infection and red cell membrane stress.