The 32-day study includes a 48-hour screening period, a 30-minute to 2-hour pre treatment period, a maximum 2-hour period for randomization and measurement of baseline values, a 24-hour treatment period, and a 96-hour post-treatment period. A 25-day follow-up period including a visit on Day 30 will take place after the active phase of the study When considered to be eligible, a first cohort of 88 patients will be randomized in a 3:1 ratio to receive 24-hrs treatment with istaroxime 0.5 μg/kg/min or placebo. If after the continuous safety monitoring and interim analyses the DMC determines that there are no safety issues with this dose, a second cohort of 88 patients will be randomized in a 3:1 ratio to receive 24-hrs treatment with istaroxime 1.0 μg/kg/min or placebo. If after the continuous safety monitoring and interim analyses of the second cohort the DMC determines that there are no safety issues with this dose, a third cohort of 88 patients will be randomized in a 3:1 ratio to receive 24-hrs treatment with istaroxime 1.5 μg/kg/min or placebo. In all cohorts, patients will receive standard of care therapy.