Background Postoperative deep vein thrombosis (DVT) is associated with significant morbidity. Even with maximal thromboprophylaxis, postoperative DVT is present in 10% of cardiac surgery patients, and is linked to receiving transfusion. We hypothesized that the incidence of DVT varies with the transfused blood product type, and increases with transfusion dose. Study design and methods 139/1070 cardiac surgery patients have DVT despite maximal chemo and mechanical prophylaxis. DVTs were detected via serial perioperative duplex venous scans (DVS). Red blood cells (RBC), platelets (PLT), plasma (FFP) and cryoprecipitate transfusion data were collected. Results Transfusion was used in 506(47%) patients: RBC [468(44%); 4.0 ± 4.2 u]; FFP [155(14.5%); 3.5 ± 2.3 u]; PLT [185(17.3%); 2.2 ± 1.3 u] and Cryoprecipitate [51(4.8%); 1.3 ± 0.6 u]. Isolated RBC transfusion accounted for 92.6% patients receiving one product, and their DVT rate was increased considerably compared to no transfusion (16.7% versus 7.3%; P < 0.001). Incidence of DVT increased substantially for multiple product transfusions; particularly when both RBC and FFP are used (25%-40%). Relative to no RBC (n = 602), multivariate logistic regression analysis identified a significant RBC-DVT dose dependent relation (P < 0.001) with: 1-3 RBC units [n = 285, AOR = 1.95(1.23-3.07), adjusted odds ratio (95% confidence interval)]; 4-6 units [n = 117; AOR = 1.65(0.86-3.20)]; and ≥ 7 RBC units [n = 66; 3.19(1.52-6.70)]. This relation also increased according to an RBC ∗ FFP interaction term [AOR = 1.87(1.11-3.22); P = 0.022]. Conclusion RBC transfusion is associated with increased risk of DVT after cardiac surgery in a dose-dependent fashion that is exacerbated when accompanied with FFP. Postoperative screening diagnostic DVS are warranted in this transfused, high risk for DVT population to facilitate timely therapeutic intervention.