© 2019 Jantti et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Introduction The prevalence of hypoalbuminemia, early changes of plasma albumin (P-Alb) levels, and their effects on mortality in cardiogenic shock are unknown. Materials and methods P-Alb was measured from serial blood samples in 178 patients from a prospective multinational study on cardiogenic shock. The association of hypoalbuminemia with clinical characteristics and course of hospital stay including treatment and procedures was assessed. Theprimary outcome was all-cause 90-day mortality. Results Hypoalbuminemia (P-Alb < 34g/L) was very frequent (75%) at baseline in patients with cardiogenic shock. Patients with hypoalbuminemia had higher mortality than patients with normal albumin levels (48% vs. 23%, p = 0.004). Odds ratio for death at 90 days was 2.4 [95% CI 1.5–4.1] per 10 g/L decrease in baseline P-Alb. The association with increased mortality remained independent in regression models adjusted for clinical risk scores developed for cardiogenic shock (CardShock score adjusted odds ratio 2.0 [95% CI 1.1–3.8], IABPSHOCK II score adjusted odds ratio 2.5 [95%CI 1.2–5.0]) and variables associated with hypoalbuminemia at baseline (adjusted odds ratio 2.9 [95%CI 1.2–7.1]). In serial measurements,albumin levels decreased at a similar rate between 0h and 72h in both survivors andnonsurvivors (ΔP-Alb -4.6 g/L vs. 5.4 g/L, p = 0.5). While the decrease was higher for patients with normal P-Alb at baseline (p 0.001 compared to patients with hypoalbuminemia at baseline), the rate of albumin decrease was not associated with outcome. Conclusions Hypoalbuminemia was a frequent finding early in cardiogenic shock, and P-Alb levels decreased during hospital stay. Low P-Alb at baseline was associated with mortality independently of other previously described risk factors. Thus, plasma albumin measurement should be part of the initial evaluation in patients with cardiogenic shock.