Use of frog ventricle to examine mechanical and electrical activity of heart.

This report describes a Langendorff heart preparation, which utilizes frog rather than mammalian hearts to demonstrate both mechanical and electrical events of the cardiac cycle. The preparation is durable in that it can be maintained for several hours while being perfused with room-temperature solutions that are not supplemented with oxygen. Ventricular perfusion is achieved via a fluid-filled reservoir coupled to a truncus arteriosus catheter advanced into the ventricle. By varying the height of the reservoir relative to the heart, changes in ventricular pressure and the rate of ventricular pressure change during systole can be recorded by way of a side port on the catheter tubing. The former is indicative of Starling's law of the heart, whereas the latter is reflective of the contractility. Electrical activity of the heart can be observed by measuring injury potentials via a needle electrode inserted into the ventricle. These are extracellular potentials that reflect ventricular action potentials. In addition, surface electrodes placed on the ventricle can be used to detect an integrated ventricular electrocardiogram. Recording of ventricular pressure simultaneously with at least one of these two electrical recordings allows a direct comparison of electrical and mechanical events of the heart. In summary, the Langendorff frog heart preparation is economical in terms of both financial cost and simplicity; yet it enables a thorough examination of both electrical and mechanical properties of the heart either as a student lab exercise or as a classroom demonstration.