Cardiorenal syndrome type 1 and cardiorenal syndrome type 3. (a) Cardiorenal syndrome (CRS) type 1 is characterized by acute worsening of heart function leading to acute kidney injury (AKI) and/or dysfunction. Acute cardiac events that may contribute to AKI include acute decompensated heart failure, acute coronary syndrome, cardiogenic shock and cardiac surgery-associated low cardiac output syndrome. (b) CRS type 3 is characterized by acute worsening of kidney function leading to acute cardiac injury and/or dysfunction, such as acute myocardial infarction, congestive heart failure, or arrhythmia. Conditions that may contribute to this syndrome include cardiac surgery-associated AKI, AKI after major noncardiac surgery, contrast-induced AKI, other drug-induced nephropathies, and rhabdomyolysis. ACE, angiotensin-converting enzyme; GFR, glomerular filtration rate; RAA, rennin-angiotensin-aldosterone.