The heart is a muscular organ, in all vertebrates responsible for pumping blood through the blood vessels by repeated, rhythmic contractions, or a similar structure in annelids, mollusks, and arthropods.
The term cardiac (as in cardiology) means related to the heart and comes from the Greek καρδία, kardia, for heart.
The heart of a vertebrate is composed of cardiac muscle, an involuntary muscle tissue which is found only within this organ. The average human heart beating at 72 BPM, will beat approximately 2.5 billion times during a lifetime spanning 66 years.
It is unknown how blood in the embryo circulates for the first 21 days in the absence of a functioning heart, although some have hypothesized that the heart is not so much a pump, as a hydraulic ram -- an organ built-up from cumulative peripheral activity.
When the human embryonic heart begins beating -- around 21 days after conception, or five weeks after the last normal menstrual period (LMP), which is the date normally used to date 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 linearly for the first month of beating, peaking at 165-185 BPM during the early 7th week, (early 9th week after the LMP).
This acceleration is approximately 3.3 BPM per day, or about 10 BPM every three days, an increase of 100 BPM in the first month.
After peaking at about 9.2 weeks after the LMP, it decelerates to about 152 BPM (+/-25 BPM) during the 15th week after the LMP.
After the 15th week the deceleration slows reaching an average rate of about 145 (+/-25 BPM) BPM at term.
The regression formula which describes this acceleration before the embryo reaches 25 mm in crown-rump length or 9.2 LMP weeks is Age in days = EHR(0.3)+6
There is no difference in male and female heart rates before birth