This editorial introduces a special issue of the International Journal of Nephrology dedicated to the cardiorenal syndrome (CRS). The issue marks a significant advancement in understanding the complex interactions between heart and kidney diseases. The CRS was officially defined at a 2009 consensus conference, characterizing five forms of heart-kidney interaction: Type I (acute heart failure associated with acute kidney injury), Type II (chronic heart failure associated with chronic kidney disease), Type III (acute kidney injury associated with acute heart failure), Type 4 (chronic kidney disease driven by chronic heart failure), and Type 5 (concomitant development of both kidney and heart failure). The editorial emphasizes the importance of this classification due to the high prevalence of cardiovascular disease (CVD) and chronic kidney disease (CKD), which often overlap. It highlights the need for further research to understand the bidirectional and dynamic interactions between the heart and kidneys, including hemodynamic changes and widespread inflammation. The special issue aims to provide insights into diagnostic aids, potential therapies, and areas requiring further investigation.This editorial introduces a special issue of the International Journal of Nephrology dedicated to the cardiorenal syndrome (CRS). The issue marks a significant advancement in understanding the complex interactions between heart and kidney diseases. The CRS was officially defined at a 2009 consensus conference, characterizing five forms of heart-kidney interaction: Type I (acute heart failure associated with acute kidney injury), Type II (chronic heart failure associated with chronic kidney disease), Type III (acute kidney injury associated with acute heart failure), Type 4 (chronic kidney disease driven by chronic heart failure), and Type 5 (concomitant development of both kidney and heart failure). The editorial emphasizes the importance of this classification due to the high prevalence of cardiovascular disease (CVD) and chronic kidney disease (CKD), which often overlap. It highlights the need for further research to understand the bidirectional and dynamic interactions between the heart and kidneys, including hemodynamic changes and widespread inflammation. The special issue aims to provide insights into diagnostic aids, potential therapies, and areas requiring further investigation.