There are a number of different cardiac emergencies that can face the neonatologist. Many of these relate to the initial presentation of congenital cardiac lesions (incidence 6–13 per 1,000 live births) (Reller et al. 2008; Ishikawa et al. 2011; Ferencz et al. 1985). Rarer causes also include cardiac arrhythmias (1 in 25,000 for supraventricular tachycardia) (Dubin 2000) and cardiomyopathies (5–9 per 100,000 infants) (Nugent et al. 2003; Lipshultz et al. 2003) which can lead to hemodynamic decompensation in the neonate. Furthermore, iatrogenic injuries caused by interventions can lead to emergencies such as cardiac tamponade. These particular pathologies can present acutely and require prompt treatment by the attending physician. For the purposes of this chapter, the pathologies are split into four common presentations with the aim of providing a practical approach to cardiac emergencies in newborns. • Shock/circulatory failure • Cyanosis • Acute heart failure • Arrhythmias