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Objective To examine the exposure-response relations between cumulative evening and night shifts and incident myocardial infarction among hospital employed health care workers, including nurses, physicians, and others.Material and Methods This national register-based cohort study includes all newly hired health care workers ever working evening or night shifts with day by day payroll information on evening and night shifts, from 2008/2009 to 2020. In total, we included 137 184 health care workers (mean age 33.3 years at inclusion, 77% women) who were followed from first registered evening or night shift for an average of 6.4 years. First time hospital contacts for myocardial infarction were identified in national health registers. Incidence rates of myocardial infarction by cumulative evening and night shifts were estimated by Poisson regression adjusted for sex, age, calendar year, diabetes, obesity, hypertension, hypercholesterolemia, education, and family history of cardiovascular disease; and for a subset of 13 080 workers, additionally adjusted for self-reported smoking, body mass index, and alcohol consumption.Results During follow-up, 477 workers (49% women) were diagnosed with myocardial infarction. Men and women showed overall incidence rates of 12.5 and 3.4 per 10 000 person years. No increasing incidence rates of myocardial infarction with cumulative number of evening or night shifts were observed.Conclusions This study of health care workers found no exposure-response relation between cumulative evening or night shifts and incident myocardial infarction during up to 13 years after the first recorded evening or night shift.