This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Heart: Cardiac Muscle, Subject name: Physiology
[{'content': 'The result of increased preload on cardiac muscle is? \nSelect and explain. \nA. Lengthening of muscle fibre, B. Shortening of muscle fibre, C. No effect, D. Variable effect', 'role': 'user'}, {'content': "Answer: A \nExplanation: ANSWER: (A) Lengthening of muscle fibreREF: Ganongs 22nd edp. 572Preload is determined by amount of blood reaching the heart; it causes an increase in the muscle fiber length and therefore according to frank starling's law increased force of contraction", 'role': 'assistant'}]