MATLAB: How to plot each local maxima of the ECG data

Question

So far I have this code, to detect the local maxima of my ECG signal by separting the ECG signal into sections of time and finding the location of each maximum. However when I run this script, I only get one maximum showing up. I would like to edit the code for it to look this, so that I get a local maxima on each line.

% Read data.
ECG = csvread('ECG.csv');
f_s = 350;
frame_duration = 0.5;
frame_len = frame_duration*f_s;
N = length(ECG);
num_frames = floor(N/frame_len);
Time = (0:length(ECG)-1)/f_s; %Number of samples divided by frequency
Amp = ECG(:,1); %ECG Amplitude
plot(Time, Amp, 'b-', 'LineWidth', 2);
xlabel('Time', 'FontSize', 20);
ylabel('ECG', 'FontSize', 20);
hold on
threshold = 100;
line(xlim, [threshold, threshold], 'Color', 'r', 'LineWidth', 2);
grid on;
for m = 1:num_frames
	index1 = (m-1)*frame_len + 1;
	index2 = frame_len*m;
	frame = Amp(index1 : index2);
	fprintf('Extracted frame #%d, from index %d to %d.\n', ...
		m, index1, index2);
	
	[max_val, indexAtMax] = max(frame);
	originalIndex = indexAtMax + index1 - 1;
	fprintf('  Max of %f occurs at index %d of cropped signal, or %d of original signal.\n', ...
	max_val, indexAtMax, originalIndex);
	if (max_val > threshold)
        
		plot(Time,Amp, Time(originalIndex),Amp(originalIndex),'r*')
		hold on
		line(xlim, [threshold, threshold], 'Color', 'r', 'LineWidth', 2);
		xlabel('Time', 'FontSize', 20);
		ylabel('ECG', 'FontSize', 20);
		grid on;
		hFig.WindowState = 'maximized'; % Maximize the window
        hold on
	end
	hold off
end

Answer 1

Remove the

hold off

in the outer loop and remove the replotting of the entire dataset in each sement processing step - change to:

plot(Time(originalIndex),Amp(originalIndex),'r*')

The code is now

% Read data.
ECG = csvread('ECG.csv');
f_s = 350;
frame_duration = 0.5;
frame_len = frame_duration*f_s;
N = length(ECG);
num_frames = floor(N/frame_len);
Time = (0:length(ECG)-1)/f_s; %Number of samples divided by frequency
Amp = ECG(:,1); %ECG Amplitude
plot(Time, Amp, 'b-', 'LineWidth', 2);
xlabel('Time', 'FontSize', 20);
ylabel('ECG', 'FontSize', 20);
hold on
threshold = 100;
line(xlim, [threshold, threshold], 'Color', 'r', 'LineWidth', 2);
grid on;
for m = 1:num_frames
	index1 = (m-1)*frame_len + 1;
	index2 = frame_len*m;
	frame = Amp(index1 : index2);
	fprintf('Extracted frame #%d, from index %d to %d.\n', ...
		m, index1, index2);
	
	[max_val, indexAtMax] = max(frame);
	originalIndex = indexAtMax + index1 - 1;
	fprintf('  Max of %f occurs at index %d of cropped signal, or %d of original signal.\n', ...
	max_val, indexAtMax, originalIndex);
	if (max_val > threshold)
        
		plot(Time(originalIndex),Amp(originalIndex),'r*')
		hold on
		line(xlim, [threshold, threshold], 'Color', 'r', 'LineWidth', 2);
		xlabel('Time', 'FontSize', 20);
		ylabel('ECG', 'FontSize', 20);
		grid on;
		hFig.WindowState = 'maximized'; % Maximize the window
        hold on
	end
	% hold off
end