Heart failure with preserved ejection fraction (HFpEF), also known as diastolic heart failure, accounts for roughly half of all heart failure cases worldwide. The condition, which occurs when the ventricles do not relax as they fill with blood following heart muscle contractions, is especially common in elderly women, striking up to 10% of those over 80 years old. Now stem cell biotech firm Novoheart Holdings Inc., of Vancouver, British Columbia, is partnering with Astrazeneca plc, of Cambridge, U.K., to co-develop a human-specific in vitro, functional model of HFpEF. The goal is to give drug researchers critical clues of a drug candidate’s efficacy before it is tested in patients.