Cardiac pacemakers powered by Betacel 147Pm nuclear batteries are undergoing clinical evaluation in Europe and the United States. This benefit/risk study analyzes the potential effects from unrestricted use of 20 000 pacemakers powered by these betavoltaic batteries. The beneficial effects of this device (lives saved and reduced medical expenses) result from improved reliability and operating lifetime (∼9 yr) compared with widely available chemical batteries of substantially shorter life ( yr). Calculated benefits are $16 800 000/yr savings to society and 76 lives (∼800 life-years) saved per year. Risks to the patient and the general population are generally less than those from natural accidents such as landslides and lightning strikes. The calculated benefit/risk ratios of 180 in terms of lives and 440 in monetary terms are in the range commonly accepted by the public.