Cardiac muscle health is dependent on the adequate supply of oxygenated blood and nutrients to ensure optimal cardiac function, avoiding ischemia. The continuous supply of oxygenated blood occurs mainly through coronary arteries embedded within the muscle. Cardiac ventricular motions involve twisting, contracting and expanding, giving rise to the biomechanical behavior of the coronary arteries. The goal of this work is to study the impact of cardiac motion on the coronary flow dynamics using a two-way fluid-structure interaction. Blood flow was modelled within an idealized 3D coronary arterial structure using incompressible laminar Navier-Stokes equations. This study was conducted on a left main artery in which the vessel walls were represented using an isotropic five-parameter Mooney-Rivlin hyperelastic material deformed dynamically with prescribed displacement boundary conditions to simulate the torsional and expansion motions. Results have shown that the bifurcation region in moving artery produced higher velocities than in the non-moving case, particularly during systolic torsional motion. During systole, the wall shear stress near the bifurcation was found to be lower in the non-moving case relative to the moving one. In the non-moving model, a helical-shaped pattern of secondary flow was observed as the blood flowed through the curved vessel. However, this pattern diminished in the moving model, where the arterial curvature dynamically changed throughout the cardiac cycle. Overall, it is necessary to include cardiac motion when modelling coronary vessels' hemodynamics.