Heart and kidney disease often coexist in the same patient, and observational 
studies have shown that cardiac disease can directly contribute to worsening 
kidney function and vice versa. Cardiorenal syndrome (CRS) is defined as a 
complex pathophysiological disorder of the heart and the kidneys in which acute 
or chronic dysfunction in one organ may induce acute or chronic dysfunction in 
the other organ. This has been recently classified into five subtypes on the 
basis of the primary organ dysfunction (heart or kidney) and on whether the 
organ dysfunction is acute or chronic. Of particular interest to the critical 
care specialist are CRS type 1 (acute cardiorenal syndrome) and type 3 (acute 
renocardiac syndrome). CRS type 1 is characterized by an acute deterioration in 
cardiac function that leads to acute kidney injury (AKI); in CRS type 3, AKI 
leads to acute cardiac injury and/or dysfunction, such as cardiac ischemic 
syndromes, congestive heart failure, or arrhythmia. Both subtypes are 
encountered in high-acuity medical units; in particular, CRS type 1 is commonly 
seen in the coronary care unit and cardiothoracic intensive care unit. This 
paper will provide a concise review of the epidemiology, pathophysiology, 
prevention strategies, and selected kidney management aspects for these two 
acute CRS subtypes.