<p>Mortality remains high amongst children with single ventricle (SV) congenital heart disease awaiting heart transplantation, especially in those with Stage 1 (S1) and Stage 2 (S2) physiology. While ventricular assist device (VAD) support has improved overall pediatric waitlist mortality, management of S1 and S2 patients with VAD continues to be challenging often leaving this already sick cohort with inadequate support options while waiting. We describe clinical deterioration of S1 and S2 patients awaiting HT and examine factors associated with clinical deterioration, waitlist mortality and post-transplant survival. This was a retrospective study of all S1 and S2 patients listed for transplant at Lucile Packard Children’s Hospital at Stanford University from November 2006 to December 2023. Clinical deterioration was defined as waitlist death or escalation of support (addition of inotropes, intubation, VAD or ECMO) between listing and waitlist removal. Logistic regression and Cox proportional hazard analyses were used to examine associations with outcomes. 61 patients (29 S1, 32 S2) were included. 58% of the patients had clinical deterioration while on the waitlist. Over a median of 79 (IQR 34-176) waitlist days, 62% were transplanted, 31% died, 5% were removed for recovery and 2% remained waiting. Of patients transplanted, 37% had clinical deterioration between listing and transplant. Of 18 patients on VAD support, 8 survived to transplant. No significant risk factors were associated with clinical deterioration on the waitlist<b>.</b> Use of total parenteral nutrition and not receiving any enteral nutrition were both significantly associated with waitlist mortality. S1 and S2 patients have high clinical disease severity at the time of listing, and over half of them progressively worsen while awaiting transplant.</p>