Background: Carcinoid heart disease (CHD) can develop in patients with carcinoid syndrome (CS), itself caused by overproduction of hormones and other products from some neuroendocrine tumours. The most common hormone is serotonin, detected as high 5-hydroxyindoleacetic acid (5-HIAA). This systematic literature review summarises current literature on the impact of CHD on survival, and the relationship between 5-HIAA levels and CHD development, progression, and mortality. Methods: MEDLINE, Embase, Cochrane databases, and grey literature were searched using terms for CHD, 5-HIAA, disease progression, and mortality/survival. Eligible articles were non-interventional and included patients with CS and predefined CHD and 5-HIAA outcomes. Results: Publications reporting on 31 studies were included. The number and disease states of patients varied between studies. Estimates of CHD prevalence and incidence among patients with a diagnosis/symptoms indicative of CS were 3–65% and 3–42%, respectively. Most studies evaluating survival found significantly higher mortality rates among patients with versus without CHD. Patients with CHD reportedly had higher 5-HIAA levels; median urinary levels in patients with versus without CHD were 266–1,381 versus 67.5–575 µmol/24 h. Higher 5-HIAA levels were also found to correlate with disease progression (median progression/worsening-associated levels: 791–2,247 µmol/24 h) and increased odds of death (7% with every 100 nmol/L increase). Conclusions: Despite the heterogeneity of studies, the data indicate that CHD reduces survival, and higher 5-HIAA levels are associated with CHD development, disease progression, and increased risk of mortality; 5-HIAA levels should be carefully managed in these patients.