Eligible are adult patients with chronic heart failure (at least 6 months) in ACC/AHA Stage C, NYHA Class III or ambulatory Class IV HF receiving maximally tolerated guideline-directed medical therapy for HF and guideline-recommended rhythm management device therapy with at least 1 hospital admission for acute worse HF requiring an intravenous diuretic within the last 12 months or elevated levels of brain natriuretic peptides. This evidence concerns the gene NPPB and hydrops fetalis.