THE DILATED heart is one of the major problems in cardiology and medicine that receives little consideration in research. Because Starling and others showed that force of contraction and work output increase in association with lengthening of the fibers of the heart muscle, we are often inclined to forget that he also demonstrated that this relationship is limited and that excessive lengthening is accompanied by rapidly progressive failure in force of contraction. The mechanism by which cardiac dilatation with lengthening of the muscle fibers increases work output and strength of contraction is unknown. Surely, recognition of the optimal degree of lengthening in the heart of intact man is not achievable today, especially with the many variables in disease states. It is possible that the relationship of fiber length (or degree of dilatation) to work output in cardiac diseases may differ considerably from that in the normal subject and among various