Cardiac rhabdomyoma is the primary feature of the genetic disease, tuberous sclerosis complex, the most common cardiac tumor diagnosed in neonates and infants. Spontaneous regression is observed in most cases, but these tumors may cause hemodynamic instability, arrhythmias or other complications. We describe the case of a critically ill neonate, resuscitated after cardiac arrest secondary to massive locally invasive cardiac rhabdomyoma, who was successfully treated with everolimus (mammalian target of rapamycin [mTOR] inhibitor). Rapid tumor regression was observed on echocardiography, but it was unlikely that it was confounded by the natural disease course of regression. The presented case suggests that mTOR inhibitors may play a significant role in the treatment of large cardiac rhabdomyomas in critically ill neonates.