This report is the first description of single ion channels from human myocardium. Using explanted human left ventricular tissue, we have studied three K-conducting and two anion-conducting channels. We report our observations of gating and ionic selectivity properties of these channels which, we argue, derive from both sarcolemmal and sarcoplasmic reticulum membranes. We postulate that one channel is the K-conducting channel (SR K channel) from human cardiac sarcoplasmic reticulum. Another channel is similar to a dimeric Cl- channel from Torpedo electroplax, displaying two equally spaced levels of open state conductance.