the heart cant pump blood so easle
some may cause diseases
DNA is part of chromosome, and will not be affected. The cell splits in chromosomes. There may be some DNAs damaged, but this is in very very small numbers.
it interrupts bloodsupply to some part of the heart causing the heart cells in the vicinity to die. If left untreated, the heart tissue will be damaged or die (infarction)
your things you love the most can be damaged
Depends on how the cell is damaged and on which organ and how it's damaged as well. Some single cells can become malignant tumores and bring about the death of the body while you might easily remove some kinds of organs without major consequence, such as one kidney, one lung, spleen etc.
it can shut down
If the concentration of molecules is higher inside the cell compared to outside, water would move into the cell to dilute the higher concentration of molecules. This may cause the cell to swell or burst. If the concentration of molecules is higher outside the cell, water would move out of the cell causing it to shrink or shrivel. The movement of water is driven by osmosis, which aims to equalize the concentration of molecules inside and outside the cell.
Some of the symptoms that come with sickle cell trait can include fever, as well as an acute form of cell degeneration that can happen throughout the body.
to check if some muscle has been damaged after heart attack surgery or injury
Animal doesn't have cell wall, they have only cell membrane. Cell wall is a rigid structure found in plant and some microbe.
Cells produce an enormous amount of molecules of which some (many) act as messengers and activators or inhibitors. When heart cells receive stimulation from other heart cells with certain molecules, they "know" what they are and that they should keep on being heart cells.
Damaged or diseased cell usually don't enter cell division anymore (some viruses can trigger cell division). By die from apoptose, followed by atrophy (natural programmed cell death). Fit cells can divide by mitosis. Or in the case of reproductive cells, meiosis.