Two pivotal aspects for achieving precise numerical simulations of cardiac electromechanics (EM) are: (i) reconstructing an accurate muscular fiber architecture that drives the electrophysiology signal and the active and passive mechanical contraction; (ii) accounting for a detailed microscale model for active force generation that governs the coupling between electrophysiology and mechanics. In this work, we introduce a 3D EM model coupled with a 0D closed-loop model of the entire cardiovascular system, addressing the two former crucial issues.. With this aim, the 3D-0D model integrates a comprehensive fiber architecture using Laplace–Dirichlet-Rule-Based-Methods (LDRBMs) and the RDQ20 microscale model for active force generation. We conduct EM simulations under physiological conditions, demonstrating the alignment of our results with experimental data found in the literature. We then carry out a systematic comparison of LDRBMs. We investigate different arrangements in cross-fibers active contraction, proving that active tension along the sheet direction counteracts myofiber contraction, while tension along the sheet-normal direction enhances cardiac work. Analysis of different myofiber architectures demonstrates the impact on ventricular pumping functionality, emphasizing the significance of transmural wall variations. Furthermore, we highlight the importance of incorporating fibers-stretch-rate feedback of RDQ20 activation model. We demonstrate its significance by comparing results obtained with and without this feature. Despite the numerical challenges it presents, the fibers-stretch-rate feedback plays a fundamental role in regulating the blood flux ejected by the ventricles. Finally, the numerical results were obtained using a realistic and anatomically accurate whole heart geometry.