First, never (unless you know what you do!) load stuff (strings, images, fonts, etc.) in draw(). It can slow down dramatically your application.
In your case, you don't aim for speed, but yet it is a good habit to take.
Declare the arrays along myValue and do the loading in setup() (removing the declararation/type part, of course).

Note: not sure why you use CSV (that can hold several data per line) and then use three files...

Next step: make a global index variable. Remove your for loops (keep the content) and increment your index variable at the end of draw(): it will do the job of iteration.
And, of course, use [yourIndex] instead of [i] or [a].

Last note: in Processing you can use float(str) instead of Float.valueOf(str).floatValue()

Mmm, it is faster to show code (untested):
Code:

float myValue;
int index; // The global index variable
String[] time;
String[] heart;
String[] speed;

void setup(){
  
  size (1200, 1000);
  frameRate(1);

  time = loadStrings("time.csv");
  heart = loadStrings("heart_rate.csv");
  speed = loadStrings("speed.csv");

}



void draw(){
 
    myValue = 10 *( float(speed[index]));
    line(index * 10, myValue * 10, myValue * 5, myValue * 5);
  
    myValue = 10 *( float(time[index]));
    ellipse(index * 10, myValue * 20, myValue * 5, myValue * 5);

    index++; // Check when reaching 120, stop or restart at 0
} 
 

Just had to change:

Code:

myValue = 10 *( float(speed[index])); 

into:

Code:

myValue = 10 * (new Float(speed[index])); 

And it's all working now.