The heart is one of the most complex and sophisticated organs in the human body. The heart is the first functional organ formed in the embryo and originates from the visceral mesoderm (Splanchnic mesoderm).

The complexity of the heart structure is far beyond people's imagination. After pre-cardiovascular mesoderm specialisation, the progeny develop bilateral heart-forming zones on both sides of the embryonic midline. The cells of the cardiogenic zone pass through the midline and fuse to the cardiac tube, which consists of two layers of cells, the myocardium and the endocardium. After that, the heart tube is looped to locate the future ventricular structure.

For a long time, scientists have successfully cultured a variety of organ-like models in vitro, but progress has been slow in cardiac organoids. Research in cardiovascular microtissue or cardiac organoids has focused on advances in cardiomyocyte engineering, such as how to engineer pre-differentiated cardiovascular cell types to mimic adult-like cardiac tissue.

These organoids replicate some aspects of human heart tissue, including stromal cells, endothelial cell network and epicardial layer, but do not reflect the process of early heart development. Therefore, the research on the morphological aspects of heart development needs to be supplemented.

Now, researchers at the Institute of Molecular Biotechnology of the Austrian Academy of Sciences say they have grown the first heart with clearly beating chambers in the laboratory. The tiny organs, or organoids, work like the hearts of 25-day-old human embryos, helping to solve many mysteries, including why babies don't scar their hearts after a heart attack.

To create heart organoids that can self-organize like cells in an embryo, the authors of the new study programmed human pluripotent stem cells, which have the ability to differentiate into any tissue, to differentiate into various types of heart cells. The team activated all six known signaling pathways involved in embryonic heart development in a specific sequence, inducing stem cells to self-organize.

As the cells differentiate, they begin to form different layers-structures that resemble the walls of a heart. After 1 week of development, the organoids are structurally equivalent to the heart of a day 25 embryo. At this stage, the heart has only one ventricle, which will become the left ventricle of the mature heart.

This human "mini heart" is smaller than a sesame seed, but can beat in a regular rhythm. Its diameter is about 2mm, including the main cell types common at this stage of development: cardiomyocytes, epithelial cells, fibroblasts and epicardium. They also have a clear ventricle that beats 60 to 100 times per minute, which is the same rate as an embryonic heart of the same age.

In fact, although humans have been able to cultivate "mini-organs" such as the brain, internal organs and liver in petri dishes for more than a decade, heart-like organs have always been a great challenge. This research breakthrough will help researchers learn more about the human heart, and it will also allow people to develop new drugs more specifically and have greater confidence in the results of clinical trials.