The human heart is an organ that provides a continuous blood circulation through the cardiac cycle and is a vital organ in the human body.[1] The heart is divided into four main chambers: the two upper chambers are called the left atrium and the right atrium (plural atria) and the two lower chambers are called the right and the left ventricle.[2] There is a thick wall of muscle separating the right side and the left side of the heart called the septum. Normally with each heartbeat, the right ventricle pumps the same amount of blood into the lungs that the left ventricle pumps out into the body. Physicians commonly refer to the right atrium and right ventricle together as the right heart and to the left atrium and left ventricle as the left heart.[3]
The electric energy that stimulates the heart occurs in the sinoatrial node, which produces a definite potential and then discharges, sending an impulse across the atria.
It is not very well known how the electric signal moves in the atria. It seems that it moves in a radial way, but Bachmann's bundle and coronary sinus muscle play a role in conduction between the two atria, which have a nearly simultaneous systole.[4][5][6] While in the ventricles, the signal is carried by specialized tissue called the Purkinje fibers which then transmit the electric charge to themyocardium.[7]
The human embryonic heart begins beating at around 21 days after conception, or five weeks after the last normal menstrual period(LMP). The first day of the LMP is normally used to date the start of the gestation (pregnancy).
The human heart begins beating at a rate near the mother’s, about 75–80 beats per minute (BPM). The embryonic heart rate (EHR) then accelerates by approximately 100 BPM during the first month to peak at 165–185 BPM during the early seventh week after conception (early ninth week after the LMP). This acceleration is approximately 3.3 BPM per day, or about 10 BPM every three days, which is an increase of 100 BPM in the first month.[8][9][10] The regression formula, which describes this acceleration before the embryo reaches 25 mm in crown-rump length, or 9.2 LMP weeks, is: the age in days = EHR(0.3)+6.[11]
After 9.1 weeks after the LMP, it decelerates to about 152 BPM (±25 BPM) during the 15th week after LMP. After the 15th week, the deceleration slows to an average rate of about 145 (±25 BPM) BPM, at term. There is no difference in female and male heart rates before birth.
The human heart and its disorders (cardiopathies) are studied primarily by cardiologists.
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