Cardiac muscle: excitability and passive electrical properties.

The field of cellular cardiac electrophysiology has made excellent progress in the last decade in its effort to understand the electrical properties of the heart. It has profited from progress in membrane electrophysiology that has increased our understanding of the basic ionic mechanisms. It has developed quantitative methods for study of these mechanisms, in spite of the geometrical complexity of the heart. Indeed this complexity has added a richness and challenge to this area. We have shared with skeletal muscle the problem of electromechanical coupling. This review has discussed the present state of our knowledge of basic membrane mechanisms of importance in understanding normal and pathological function of heart muscle. It is intended to lay the groundwork for the following articles dealing with special aspects of cardiac electrophysiology. There is a continual interchange of ideas and concepts between applied and basic electrophysiology, and, as a result of this interchange, we can expect both areas to grow greatly in the coming years.