Contrast-enhanced MR angiography (CE-MRA) is often used in cardiovascular MRI, but contrast agents can have adverse effects. This work proposes to use deep learning to reduce contrast dose by 80%. A deep neural network was trained to enhance low-dose images using a synthetically generated dataset and validated with both synthetic and real low-dose images. The method was assessed for image quality, diagnostic accuracy and confidence and accuracy of vessel measurements. Enhanced low-dose images were found to be comparable to reference high-dose data. Therefore, the method could enable a reduction in contrast dose for CMR.