When I was learning about the heart, it helped me to think of it like a cars engine. Cars have electrical systems that fire fuel injectors. The timing in the heart is electrical and when fired, produces mechanical results. When your car runs rough, the timing is off, and you use a lot of fuel. The heart is the same way. When the timing is off, the chambers don't get full, and when they contract (beat) they don't move a lot of blood. But the heart is still doing the same amount of work! People with arrythmias, have less energy, may be pale, and short of breath.
Atherosclerosis is like clogged fuel injectors. When the arteries are clogged with plaque, the fuel (oxygen and energy) can't reach the parts that need it. Infarction means death of cells. Fortunately when your car dies from poor fuel delivery,,,,the motor isn't ruined. When parts of your heart are oxygen deprived, the cells die. Most of the time, an infarction (heart attack) doesn't ruin the whole heart. It just becomes weaker. But, unlike your car, the walls of the heart can't be repaired.
Hypertension is when the pressure in the arteries is over 120/70. When the heart beats, it has to force open the aortic valve to get blood to the rest of your body. If the pressure on the other side of that valve is high, the heart has to work a lot harder. When you work a muscle a lot harder, it gets bigger. If you're a guy on the beach, big muscles are a plus. But a big muscular heart is a problem. When the heart muscle gets bigger, the chambers get smaller. Therefore, the heart pumps less blood with each beat. But, being larger, it requires more energy and oxygen to do so. People with enlarged hearts have poor endurance, and are at risk for a heart attack.
Remember those clogged arteries? Now that the heart is larger, it needs more blood----the already narrowed arteries cant supply enough and heart tissue dies.
Good Luck with your studies!