A condition that outlines the complicated interactions between heart and kidney function, in which primary disease of one organ results in dysfunction of the other. This relationship has been noted for decades but was not consistently defined. At this time, 5 subtypes of cardiorenal syndrome (CRS) are recognized.

In CRS types 1 and 2, the primary organ dysfunction is cardiac, which results in decline in renal function. CRS1 denotes acute heart failure, and CRS2 involves chronic heart failure. CRS types 3 and 4 refer to acute and chronic primary renal dysfunction resulting in heart failure. Type 5 CRS is distinct from all of these, in which an acute or chronic systemic disorder (such as sepsis) results in both renal and cardiac dysfunction.