Final answer:
The parasternal long-axis view is the best for assessing the pressure gradient across the aortic valve, as it provides a clear image of the valve and the left ventricular outflow tract.
Step-by-step explanation:
The best view for assessing the pressure gradient across the aortic valve is the parasternal long-axis view. This imaging view is specifically useful for evaluating the structure and function of the aortic valve. The parasternal long-axis view provides a clear image of the left ventricle, aortic valve, and the outflow tract. In this view, Doppler measurements can be performed to assess the flow through the aortic valve and to calculate the pressure gradient across it, which is crucial for diagnosing conditions like aortic stenosis.