Conventional 4D flow MRI requires electrocardiogram gated cine acquisition and respiration control to measure flow dynamics associated with one synthetic cardiac cycle. This often leads to low acquisition efficiency and also cannot resolve beat-by-beat nor respiratory-related flow variations. This work presents a new 4D real-time flow MRI method which is able to simultaneously resolve respiratory and cardiac motion. Compared to conventional 4D flow MRI, the proposed method well captures the beat-by-beat flow variations and respiration-related flow dynamics. Its feasibility for aortic flow was demonstrated in several healthy subjects and also patients with atrial fibrillation.