Final answer:
Heart failure is primarily caused by a decrease in contractility of the heart muscle, leading to inadequate blood circulation in the body.
Explanation:
The underlying cause of all heart failure is a decrease in contractility. When the heart muscle is weakened and cannot contract effectively, it leads to insufficient blood being pumped throughout the body. This decrease in contractility can result from conditions such as coronary artery disease, high blood pressure, and diabetes.
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