Final answer:
Patients with heart failure have symptoms due to an impairment of the cardiac muscle cells' endoplasmic reticula, resulting in a reduced contractile force of the heart.
Step-by-step explanation:
The majority of patients with heart failure have symptoms due to an impairment of the cardiac muscle cells' endoplasmic reticula. When these structures do not function properly, there is an insufficient number of calcium ions available to trigger a sufficient contractile force. As a result, the heart cannot pump with sufficient force to transport oxygenated blood to all the vital organs, leading to symptoms of heart failure.