Researchers have developed a 'FRESH' new method of 3D printing complex anatomical structures out of collagen - a primary building block in many human tissues. The method demonstrates 3D printing of complex collagen-based cardiac structures and tissues that closely mimic the form and function of those in the human heart. Despite its great potential, the widespread use of 3D printing techniques in biomedical applications has been hindered by technological limitations, including poor tissue fidelity and low print resolutions. As such, printing with living cells or creating soft biomaterials such as collagen - two highly sought-after goals - has proven difficult. Here, Andrew Lee and colleagues describe a new method to directly 3D bioprint collagen. The authors, who first put forward their FRESH approach in 2015, developed an improved, second iteration of the "freeform reversible embedding of suspended hydrogels" (FRESH v2.0) 3D bioprinting technique, which uses rapid changes in pH to cause extruded collagen to solidify with precise control. The method can create complex structural and functional tissue architectures that can be further embedded with living cells or complex vasculature at printing resolutions up to 10 micrometers. Lee et al. used this approach to create human heart parts entirely from collagen and human cells, including cardiac tissue, contractile ventricles and even a neonatal heart. Bioprinted hearts accurately reproduced patient-specific MRI anatomical structures, the authors report, following a validation study, while cardiac components printed with human cardiac muscle cells achieved advanced contractile functionality, they say. In a related Perspective, Queeny Dasgupta and Lauren Black III review past advancements in 3D bioprinting and the "unprecedented promise" Lee et al.'s work shows for the future.