Study Objectives - Spontaneous echo contrast (SEC) is visible as smoke-like wisps during echocardiography and represents a pre-clotting state. Digital greyscale measurements provide an objective measure of the degree of SEC in cardiac chamber blood. We speculate that the digital greyscale prognosticates survival following out of hospital cardiac arrest. Study Design/Methods - Multi-center, retrospective review of digitally recorded echocardiographic images from patients presenting to the emergency department following OHCA. Echo images were reviewed blinded to all clinical information for the presence of SEC using adjudication. The degree of SEC was measured using a digital analysis tool to quantify the greyscale of cardiac chamber blood. Primary outcome was survival to hospital discharge and secondary outcomes included other survival endpoints. Univariate and multivariate methods were used to measure association between SEC, greyscale measurements and survival. Results/Findings - Of the 717 patients enrolled in the study, 32.2% demonstrated SEC. Survival to hospital admission was less common for patients with SEC (9.6% vs 17.4%, p=0.0065. Survival to hospital discharge was less common in patients with SEC, but the difference did not reach statistical significance. Right ventricular (RV) greyscale measurements outperformed other cardiac chamber measurements. Patients with higher RV greyscale were less likely to demonstrate ROSC (OR 0.21, 0.05-0.85, p=0.0291) and survive to hospital admission (OR 0.14, 0.02-0.14, p=0.0230). Median digital greyscale measurements of right ventricular cardiac chamber blood were lowest for patients who survived to hospital discharge (29) and increased for those who survived to hospital admission (33), demonstrated ROSC (37) or died in the ED without ROSC (45). CONCLUSION: SEC is common following cardiac arrest. Patients with higher digital greyscale measurement of right ventricular cardiac chamber blood were less likely to demonstrate ROSC or survival to hospital admission. Right ventricular greyscale measurements could be useful in prognosticating survival following cardiac arrest.