Compared to your brain that is responsible for a lot off things including that emotion you felt when you were dumped by your ex or you dumped your ex (you know a lot of you would not admit that you were at the receiving end of a dump just like I will also not agree even when I have had my heart shattered severally), your heart does only one job which is to act like the pumping machine in your house.
The heart is the body's pumping machine and unlike the literal saying of your heart being broken, that organ doesn't have any emotion have intend to give you an emotional attachment in the future. It's job is just to pump the blood it receives to whatever organ it is connected to. Sincerely, if the heart wasn't connected to the lungs but instead to the brain, it would have done the same job of pumping blood directly to the brain but thank goodness that anatomy did the right thing of connecting one valve to the lungs so we can oxygenate bloods that are sent there for the heart to pump the oxygenated blood to the body.
That throbbing muscle is actually the pump that powers the entire circulatory system transporting blood, nutrients, oxygen, hormones, heat, immune cells, and it also transport things that needs to removed from the body like waste and carbon dioxide. For the heart to pump blood out of itself, it generates a high hydrostatic pressure, and to allow blood flow into it, a low pressure and it is this gradient of force that is regarded as a blood pressure.
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Talking about blood pressure, that strain your arteries feel when your heart move blood around your body which is normally 60 beats per minutes up to 5 liters of blood is the normal for everyone. Do the math yourself for the total amount of beat your heart does a day; Oh! you want me to help you? Okay, your heart beats 100,000 beats a day, and 35 million beats a year with about 2 to 3 billion beats in a lifetime based on the life expectancy.
Okay, now for a quick anatomy, that heart of yours isn't as big as your head, on a contrary, it is just the size of 2 fist joined together. That organ of yours is vaguely cone-shaped weighing about 250 to 350 grams. I do not know which you were told, left or right. The fact remains that the heart is in the middle of the chest, in the mediastinum area between those lungs of yours but it has one angle pointing inferior towards the left hip and posterior towards the right shoulder.
For such an organ to be able to hold such pressure then you need to understand that it is nestled in a double-walled sac known as the pericardium with its outer layer which is referred to as the fibrous pericardium is made of dense connective tissues which protects the heart while also doing the job of an anchor to other tissues so it is firm.
The inner serous pericardium includes the inner visceral pericardium and an outer parietal pericardium and they are separated by fluid which provides a slippery environment for the heart to move around in preventing friction. Don't forget that the wall of the heart is made up of three tissues, the epicardium which is the outermost, the myocardium which is the middle, and the endocardium which is the innermost.
Some of you do not know but your heart is divided laterally into two sides by a thin partition which is known as the septum creating two superior atria and two inferior ventricles. The atria are the area for low pressure while the ventricles are the area for high pressure. These chambers have valves that allow for either entry or exit, once a blood exits from one, it is not allowed into the chamber again and when it enters from the other, it cannot go out from there again.
Those said, when the heart experience cardiac arrest, there are things that can be done contrary to what we are made to believe in movies. In movies, a defibrillator can be used to restored an already stopped heart but this isn't true with medicine at all but before then when a person is experiencing a cardiac arrest, CPR can help prolong heart function but this cannot save a person without the help of a defibrillator. Another thing is that the heart isn't turned on when a defibrillator is used, rather it is restarts the heart something like turning it off and on as quick as possible.
Just like the skeletal muscle, the cardiac muscle is striated and uses the sliding filaments to contract but that's where their similarities end, from formation to the amount of energy-generating mitochondria, everything between the the both muscles are different and the heart is made up of up to 30% of mitochondria and that is while it can beat for a very long time without being stressed.
Defibrillator is used when the heart beat is our of sync known as fibrillation which can be caused by a lot of things including a heart attack and this is when a defibrillator is introduced to send electrical charges triggering action potential in all the cells thereby causing the cells to re-polarize, leaking again leading to a synchronized rhythm of the heart again.
Reference
https://www.nhlbi.nih.gov/health/heart/anatomy
https://training.seer.cancer.gov/anatomy/cardiovascular/heart/structure.html
https://emedicine.medscape.com/article/1948510-overview?form=fpf
https://www.nhlbi.nih.gov/health/defibrillators
https://www.ncbi.nlm.nih.gov/books/NBK499899/
https://www.ncbi.nlm.nih.gov/books/NBK572070/
https://www.ncbi.nlm.nih.gov/books/NBK535355/