# Valve cells are crucial for efficient cardiac performance in Drosophila

## TL;DR

This study shows that two specialized valve cells in fruit fly hearts are crucial for efficient blood flow and overall heart performance.

## Contribution

The physiological role of intracardiac valve cells in Drosophila is experimentally elucidated for the first time.

## Key findings

- Malformed or damaged cardiac valves in Drosophila reduce heart performance and blood transport capacity.
- Reduced luminal opening at the valve region is a main cause of impaired heart function.
- Intracardiac hemolymph flow patterns resemble those in vertebrates, suggesting conserved fluid dynamics.

## Abstract

Blood flow in metazoans is regulated by the activity of the heart. The open circulatory system of insects consists of relatively few structural elements that determine cardiac performance via their coordinated interplay. One of these elements is the intracardiac valve between the aorta and the ventricle. In Drosophila, it is built by only two cells, whose unique histology represents an evolutionary novelty. While the development and differentiation of these highly specialised cells have been elucidated previously, their physiological impact on heart performance is still unsolved. The present study investigated the physiological consequences of cardiac valve malformation in Drosophila. We show that cardiac performance is reduced if valves are malformed or damaged. Less blood is transported through the heart proper, resulting in a decreased overall transport capacity. A reduced luminal opening was identified as a main reason for the decreased heart performance in the absence of functional valves. Intracardiac hemolymph flow was visualised at the valve region by microparticle injection and revealed characteristic similarities to valve blood flow in vertebrates. Based on our data, we propose a model on how the Drosophila intracardiac valves support proper hemolymph flow and distribution, thereby optimising general heart performance.

Blood flow in metazoans is regulated by the heart’s activity. Insects possess an open circulatory system with a few structural components that collectively influence cardiac performance. A key element is the intracardiac valve between the aorta and the ventricle, which in Drosophila consists of only two specialised cells, representing an evolutionary innovation. While the development of these cells has been studied, their physiological impact on heart function is less understood. This study investigates the consequences of cardiac valve malformation in Drosophila. Our findings indicate cardiac performance declines when the valves are malformed or damaged, leading to decreased blood transport and lower overall capacity. A reduced luminal opening contributes significantly to diminished heart performance without functional valves. Moreover, the visualisation of intracardiac fluid flow using microparticle injection reveals similarities to blood flow in vertebrates. Based on these insights, we propose a model detailing how intracardiac valves optimise fluid flow and enhance insect heart performance.