Cardiorenal syndromes (CRS) have been subclassified as five defined entities 
which represent clinical circumstances in which both the heart and the kidney 
are involved in a bidirectional injury and dysfunction via a final common 
pathway of cell-to-cell death and accelerated apoptosis mediated by oxidative 
stress. Types 1 and 2 involve acute and chronic cardiovascular disease (CVD) 
scenarios leading to acute kidney injury or accelerated chronic kidney disease. 
Types 2 and 3 describe acute and chronic kidney disease leading primarily to 
heart failure, although it is possible that acute coronary syndromes, stroke, 
and arrhythmias could be CVD outcomes in these forms of CRS. Finally, CRS type 5 
describes a simultaneous insult to both heart and kidneys, such as sepsis, where 
both organs are injured simultaneously. Both blood and urine biomarkers are 
reviewed in this paper and offer a considerable opportunity to enhance the 
understanding of the pathophysiology and known epidemiology of these recently 
defined syndromes.