A renally active substance from heart muscle and from blood.

1. A steroid-like compound has been isolated from cat heart muscle by thin-layer chromatography.2. This compound has been characterized by measurement of its R(F) values in two solvent systems.3. No similar substance could be detected in the 1 hr venous outputs of cat adrenals.4. It could not be detected in heart-lung circuit blood when the heart had been perfusing for 1(1/4)-1(1/2) hr at constant venous input and peripheral resistance. The compound was however extractable from the circuit blood 10-15 min after reduction in venous input.5. The actions of this compound on the isolated kidney resemble those of aldosterone but are of much shorter latency.6. The heart substance differs from aldosterone in R(F) values and has more than 10 times the renal activity of aldosterone when the two substances are equated (visually) for ability to reduce blue tetrazolium.