Nutritional rickets is still occasionally found in high-income countries, especially in populations at risk, and induced hypocalcaemia is a rare but possible cause of dilated cardiomyopathy. Although rare, physicians need to consider nutritional rickets in the differential diagnosis of hypocalcaemia cardiac failure, especially in high-risk populations such as immigrants. Despite being a reversible condition, the prognosis depends on the severity and time of diagnosis. We report two cases of exclusively breastfed infants with congestive cardiac failure due to hypokinetic dilated cardiomyopathy who had completely different outcomes. This report supports the need for prevention of this deficiency and underlies the role of vitamin D supplementation.