Abstract The complex interplay between the cardiovascular and renal systems has received significant clinical, translational, and basic research attention over the past 2 decades In both the acute and chronic care settings, dysfunction of either the heart or the kidneys can lead to dysfunction of the other organ While this interaction has been obvious and well known in severe cases (e.g., advanced kidney failure leading to hyperkalemia and resultant cardiac dysrhythmias), recent understanding of less severe or even subclinical interactions with profound bidirectional effects have been realized This chapter reviews these interactions under the construct of the cardiorenal syndromes, with a focus on acute and chronic renal consequences of cardiac disease, and on potential novel diagnostic and therapeutic maneuvers to improve patient outcomes Keywords Cardiorenal syndrome; acute kidney injury; children; heart failure; dialysis Introduction The complex interplay between the cardiovascular and renal systems has received significant clinical, translational, and basic research attention over the past 2 decades In both the acute and chronic care settings, dysfunction of either the heart or the kidneys can lead to dysfunction of the other organ While this interaction has been obvious and well known in severe cases (e.g., advanced kidney failure leading to hyperkalemia and resultant cardiac dysrhythmias), recent understanding of less severe or even subclinical interactions with profound bidirectional effects have been realized This chapter reviews these interactions under the construct of the cardiorenal syndromes, with a focus on acute and chronic renal consequences of cardiac disease, and on potential novel diagnostic and therapeutic maneuvers to improve patient outcomes Classification of the Cardiorenal Syndromes The Acute Dialysis Quality Initiative convened a consensus conference in 20081 to codify heart-kidney interactions into five distinct cardiorenal syndrome categories (Table 78.1) The cardiorenal syndromes are categorized as either acute or chronic, and whether the heart or kidney is the primary organ that is injured, or whether both are injured secondary to a systemic process Table 78.1 Classification of Cardiorenal Syndrome Types and Associated Clinical Syndromes Acute Primary Secondary Dysfunction Dysfunction Cardiac AKI Chronic Cardiac AKI or CKD Acute Renal Acute heart dysfunction or injury Chronic Renal Chronic cardiac dysfunction Acute/Chronic Systemic Type Time Course Both Clinical Syndromes Acute decompensated heart failure Cardiogenic shock Acute coronary syndrome LV dysfunction Diastolic dysfunction Cardiomyopathy Cardiopulmonary bypass Primary acute kidney disease leading to volume overload/electrolyte disturbance Contrast nephropathy Chronic hypertension Cardiac calcifications Left ventricular hypertrophy Systemic collagen vascular disease Oncologic disease Sepsis AKI, Acute kidney injury; CKD, chronic kidney disease; LV, left ventricular Acute Cardiorenal Syndromes: Type 1 and Type The acute cardiorenal syndromes present significant challenges in patient management because recognition of acute disease can be delayed, and interventions can be invasive and sometimes exacerbate the clinical problem