A multiple sequence alignment heatmap displays amino acid residues across aligned protein sequences, with rows representing individual chains by PDB code and columns indicating alignment positions. Each cell is colored according to its amino acid type using a custom d3.scaleOrdinal palette. The visualization uses d3.csv to load data, d3.scaleBand for axes, and d3-tip to show tooltips detailing the residue number and chain information on hover. Rendered as SVG rectangles with mouseover interactions, the chart includes a title and axis labels.