Over the last decade, it has become increasingly clear that the cardiovascular 
and renal systems are interdependent. Primary disorders of either system have 
been shown to disturb the other system. As a result, a class of cardiorenal 
syndrome (CRS) has been identified where in a vicious cycle is established in 
which acute/chronic dysfunction of either the kidney or the heart exacerbates 
the loss of function in the other organ. The ADQI organization has proposed a 
classification derived from a consensus conference held in 2008. CRS is 
classified as a disorder of the heart and kidneys whereby acute or chronic 
dysfunction in one organ may induce acute or chronic dysfunction in the other. 
The general definition has been expanded into five subtypes: CRS type 1 = acute 
worsening of heart function (acute heart failure-acute coronary syndrome) 
leading to kidney injury and/or dysfunction; CRS type 2 = chronic abnormalities 
in heart function (chronic heart failure-chronic heart disease) leading to 
kidney injury or dysfunction; CRS type 3 = acute worsening of kidney function 
(acute kidney injury) leading to heart injury and/or dysfunction; CRS type 4 = 
chronic kidney disease (chronic kidney disease) leading to heart injury, disease 
and/or dysfunction; and CRS type 5 = systemic conditions leading to simultaneous 
injury and/or dysfunction of heart and kidney. A major problem with previous 
terminology was that it did not allow for identification of pathophysiological 
interactions occurring in the different types of combined heart/kidney 
disorders. The subdivision into different subtypes seems to provide a better 
approach to this syndrome.