Heart disease is the leading cause of death worldwide, but a team of scientists at QIMR Berghofer is on a mission to find ways to repair damaged heart tissue.  To help achieve this ultimate goal, they're growing tiny living and beating models of human heart muscle in the lab. These cardiac organoids are no bigger than a chia seed, but closely mimic the real organ so the researchers can study the heart's biology and test new therapeutics.  Professor James Hudson explains how the team's latest advance introduces a vascular system to the tiny heart models for the first time which has already proved to be a gamechanger for their research.