Hypophosphatemia has been found to be associated with multiple organ dysfunction. In this study we aimed to investigate the association between low serum phosphorus and acute heart failure. A total of 213 subjects, 101 patients with acute heart failure and 112 healthy subjects were included in this case-control study. Serum phosphorus levels, calcium levels, and PTH concentrations were measured. Ejection fraction percentages, pulse rates, systolic and diastolic blood pressures were recorded. The groups were similar in terms of age and gender (p=0.067 and 0.995, respectively). The phosphorus levels and ejection fraction percentages of the patients with heart failure were lower than for the healthy subjects (p<0.001). Frequency of hypophosphatemia was higher in the heart failure group (p<0.001). There was a strong relationship between low serum phosphorus level and acute heart failure (OR 9.85, CI 95% 3.6-26.3, p<0.001). The phosphorus level of patients with acute heart failure was found to be low in this study. Therefore, the phosphorus level should be controlled in patients with acute heart failure and phosphorus supplementation can be a complimentary treatment for these patients.