Cardiac defects upon heart-specific ribonucleic acid interference (RNAi) knockdown are seen in Drosophila. (A) Wild-type dorsal heart tube stained with the F-actin stain phalloidin. The magnified region (right) is highlighted. Arrowheads point to ostia (inflow tracks), and the arrow shows the circumferential orientation of myofibrils. (B) Cka/Striatin RNAi induces myofibrillar disarrangement. Myofibrils are oriented in a disorganized, mainly anterior-posterior orientation with gaps in between (arrow). (C) Knockdown of NACα/NACA causes severe cardiac tissue disintegration. Adult cardiomyocyte tissue may be completely absent (asterisk), whereas some heart-associated longitudinal muscles are still present (arrowheads). At larval stages, the heart is much less affected, suggesting a maturation or remodeling defect. (D) Knockdown of EcR/NR1H blocks cardiac remodeling and causes myofibrillar disarray (arrow). Ventral longitudinal muscles are also abnormal (arrowhead).