Participants with known congestive heart failure (CHF); if known, patients with left ventricular ejection fraction (LVEF) =< 40% are excludedXx_NEWLINE_xXLeft ventricular ejection fraction (LVEF) >= 55%Xx_NEWLINE_xXPediatric patients: normal left ventricular function with ejection fraction > 55% or shortening fraction >= 27%Xx_NEWLINE_xXLeft ventricular ejection fraction (LVEF) >= institutional lower limit of normalXx_NEWLINE_xXLeft ventricular ejection fraction >= 45%Xx_NEWLINE_xXSystolic cardiac function will be assessed at screening if clinically indicated by history and physical; only patients with left ventricular ejection fraction (LVEF) >= 50% will be eligible for enrollmentXx_NEWLINE_xXLeft ventricular ejection fraction (LVEF) >= 50% (measured within 28 days of study entry)Xx_NEWLINE_xXPatients must have left ventricular ejection fraction (LVEF) > 45% or within institutional normal limitsXx_NEWLINE_xXLeft ventricular ejection fraction (LVEF) < 50%, regardless of whether there are symptoms of heart failureXx_NEWLINE_xXLeft ventricular ejection fraction (LVEF) >= 50%Xx_NEWLINE_xXIf cardiac function assessment is clinically indicated or performed: participants will be ineligible if left ventricular ejection fraction (LVEF) is less than normal per institutional guidelines, or < 55%, if the threshold for normal is not otherwise specified by institutional guidelinesXx_NEWLINE_xX