OBJECTIVES. Evaluation of the effect of selected work environment factors on a sea-going ship on the occurrence of a sudden cardiac event and its recognition as a work-related accident. BACKGROUND. Sudden cardiac events, myocardial infarction in particular, among crews of seagoing ships are the most frequent reasons for fatal morbid events. In more than 20% of such cases, conditions and organization of work at sea are found to be of essential importance. Problems with certification are related with the assessment of the significance and impact of specific work environment factors overlapping with classic genetic and environmental factors of diseases of atherosclerotic origin. MATERIAL AND METHODS. The analysis embraced medical documentation on the state of health and working conditions at sea concerning 30 crewmembers of Polish sea-going vessels, who had suffered from sudden cardiac events in the years 1998-2009. The impact of selected work environment factors on the legitimacy of legal recognition of the event as a work-related accident was analysed by Fisher's test and multi-factorial regression. RESULTS. The presence of classic genetic and environmental risk factors of cardiovascular events was confirmed in all persons examined. A significant effect on destabilization of the disease, deterioration of health, and the occurrence of a sudden circulation event was shown to be strictly related with isometric and dynamic effort, particularly with heat discomfort in the maritime work environment. This satisfied the legal criteria for recognition of a work-related accident in half of the cases examined. CONCLUSIONS. Isometric and dynamic effort associated with work under heat stress conditions may be regarded as a decisive causative factor for a sudden cardiac event and the recognition of a work-related accident at sea.