How do conjoined twins share one heart?

Conjoined twins share one heart when their embryonic development is altered, resulting in the fusion of their heart structures. This typically occurs when the zygote splits incompletely during the early stages of development, leading to the formation of two individuals with interconnected organs. The shared heart can lead to complex physiological challenges, as both twins depend on the single organ for circulation, which can affect their survival and health. The extent of sharing varies, with some pairs having more integrated circulatory systems than others.